chore: remove dead {$IFDEF FPC} blocks, --cache-dir, and migrate_full.py

The compiler has been self-hosting since v0.7.0 and FPC is no longer
part of the toolchain. Remove the last FPC-conditional code paths:

- Blaise.pas: drop CacheKeyForFile, LoadCachedIR, StoreCachedIR and
  both {$IFDEF FPC} whole-program IR cache blocks; remove --cache-dir
  flag and CacheDir/UnitIR/UnitName/UnitPath locals; collapse the
  ReadProcessChunk FPC/Blaise fork to the Blaise implementation only;
  drop the poUsePipes/poStderrToOutPut Options block.

- tools/migrate_full.py: deleted — the Python migration analyser is no
  longer needed now that the toolchain is fully Blaise-native.

compiler/src/main/pascal/Blaise.pas

@@ -45,7 +45,6 @@ begin
   WriteLn('  --target <id>       linux-x86_64 (default), macos-arm64');
   WriteLn('  --emit-ir           Print QBE IR to stdout and exit');
   WriteLn('  --debug-opdf        Emit OPDF debug info (.opdf.s companion file)');
-  WriteLn('  --cache-dir <dir>   Directory for per-unit IR cache (speeds up incremental builds)');
   WriteLn('');
   WriteLn('Configuration:');
   WriteLn('  Unit search paths can also be set in blaise.cfg (one unit-path=<dir>');
@@ -109,7 +108,7 @@ begin
     else if StrHead(Arg, 3) = '-FE' then
       OutDir := StrCopyTail(Arg, 3)
     else if StrHead(Arg, 3) = '-FU' then
-      { unit cache directory — ignored in Phase 1 }
+      { unit output directory — ignored }
     else if StrHead(Arg, 3) = '-Fu' then
       SearchPaths.Add(StrCopyTail(Arg, 3))
     else if StrHead(Arg, 2) = '-o' then
@@ -182,8 +181,7 @@ function ParseArgs(
   out OutputFile:  string;
   out EmitIR:      Boolean;
   out OPDFEnabled: Boolean;
-  out SearchPaths: TStringList;
-  out CacheDir:    string): Boolean;
+  out SearchPaths: TStringList): Boolean;
 var
   I: Integer;
   Arg: string;
@@ -193,7 +191,6 @@ begin
   OutputFile  := '';
   EmitIR      := False;
   OPDFEnabled := False;
-  CacheDir    := '';
   SearchPaths := TStringList.Create;
 
   I := 1;
@@ -215,11 +212,6 @@ begin
       Inc(I);
       SearchPaths.Add(ParamStr(I));
     end
-    else if (Arg = '--cache-dir') and (I < ParamCount) then
-    begin
-      Inc(I);
-      CacheDir := ParamStr(I);
-    end
     else if Arg = '--emit-ir' then
       EmitIR := True
     else if Arg = '--debug-opdf' then
@@ -256,100 +248,10 @@ begin
   Result := True;
 end;
 
-{$IFDEF FPC}
-{ Returns a cache key string for the given source file: "<mtime>:<size>".
-  Returns '' if the file cannot be stat'd. }
-function CacheKeyForFile(const APath: string): string;
-var
-  SR: TSearchRec;
-begin
-  Result := '';
-  if FindFirst(APath, faAnyFile, SR) = 0 then
-  begin
-    Result := IntToStr(SR.Time) + ':' + IntToStr(SR.Size);
-    FindClose(SR);
-  end;
-end;
-
-{ Try to load cached IR for a unit.  Returns '' on cache miss. }
-function LoadCachedIR(const ACacheDir, AUnitName, ASourcePath: string): string;
-var
-  IRFile, KeyFile: string;
-  StoredKey, CurrentKey: string;
-  SL: TStringList;
-begin
-  Result := '';
-  if ACacheDir = '' then Exit;
-  IRFile  := IncludeTrailingPathDelimiter(ACacheDir) + AUnitName + '.ssa';
-  KeyFile := IRFile + '.key';
-  if not FileExists(IRFile) or not FileExists(KeyFile) then Exit;
-  CurrentKey := CacheKeyForFile(ASourcePath);
-  if CurrentKey = '' then Exit;
-  SL := TStringList.Create;
-  try
-    SL.LoadFromFile(KeyFile);
-    StoredKey := Trim(SL.Text);
-  finally
-    SL.Free;
-  end;
-  if StoredKey <> CurrentKey then Exit;
-  SL := TStringList.Create;
-  try
-    SL.LoadFromFile(IRFile);
-    Result := SL.Text;
-  finally
-    SL.Free;
-  end;
-end;
-
-{ Write IR and its cache key to the cache directory. }
-procedure StoreCachedIR(const ACacheDir, AUnitName, ASourcePath, AIR: string);
-var
-  IRFile, KeyFile: string;
-  Key: string;
-  SL: TStringList;
-begin
-  if ACacheDir = '' then Exit;
-  if not ForceDirectories(ACacheDir) then Exit;
-  Key     := CacheKeyForFile(ASourcePath);
-  if Key = '' then Exit;
-  IRFile  := IncludeTrailingPathDelimiter(ACacheDir) + AUnitName + '.ssa';
-  KeyFile := IRFile + '.key';
-  SL := TStringList.Create;
-  try
-    SL.Text := AIR;
-    SL.SaveToFile(IRFile);
-  finally
-    SL.Free;
-  end;
-  SL := TStringList.Create;
-  try
-    SL.Text := Key;
-    SL.SaveToFile(KeyFile);
-  finally
-    SL.Free;
-  end;
-end;
-{$ENDIF}
-
 function ReadProcessChunk(AProc: TProcess): string;
-{$IFDEF FPC}
-const
-  BufSize = 4096;
-var
-  Buf: array[0..4095] of Byte;
-  N:   Integer;
-begin
-  N := AProc.Output.Read(Buf, BufSize);
-  Result := '';
-  if N > 0 then
-    Result := StrHead(string(PChar(@Buf[0])), N);
-end;
-{$ELSE}
 begin
   Result := AProc.ReadOutput
 end;
-{$ENDIF}
 
 function RunProcess(const AExe: string; AArgs: TStringList;
   out AOutput: string): Integer;
@@ -361,9 +263,6 @@ begin
   Proc := TProcess.Create(nil);
   try
     Proc.Executable := AExe;
-{$IFDEF FPC}
-    Proc.Options := [poUsePipes, poStderrToOutPut];
-{$ENDIF}
     for I := 0 to AArgs.Count - 1 do
       Proc.Parameters.Add(AArgs.Strings[I]);
     Proc.Execute;
@@ -458,7 +357,6 @@ var
   EmitIR:      Boolean;
   OPDFEnabled: Boolean;
   OPDFAsmFile: string;
-  CacheDir:    string;
   Source:   TStringList;
   Lexer:    TLexer;
   Parser:   TParser;
@@ -470,16 +368,12 @@ var
   Units:    TObjectList;
   I:        Integer;
   IR:       string;
-  UnitIR:   string;
   IRFile:   string;
-  UnitName: string;
-  UnitPath: string;
 
 begin
   SearchPaths := nil;
   OPDFEnabled := False;
   OPDFAsmFile := '';
-  CacheDir    := '';
   if IsFPCStyleInvocation then
   begin
     if not ParseFPCArgs(SourceFile, OutputFile, SearchPaths, OPDFEnabled) then
@@ -491,7 +385,7 @@ begin
   end
   else
   begin
-    if not ParseArgs(SourceFile, OutputFile, EmitIR, OPDFEnabled, SearchPaths, CacheDir) then
+    if not ParseArgs(SourceFile, OutputFile, EmitIR, OPDFEnabled, SearchPaths) then
     begin
       PrintUsage;
       Halt(1);
@@ -578,83 +472,21 @@ begin
     end;
 
     try
-      {$IFDEF FPC}
-      { IR caching — FPC-only; uses TSearchRec etc. not available under Blaise }
-      if CacheDir <> '' then
-      begin
-        UnitIR := CacheKeyForFile(SourceFile);
-        if Units <> nil then
-          for I := 0 to Units.Count - 1 do
-          begin
-            UnitName := TUnit(Units.Items[I]).Name;
-            UnitPath := TUnit(Units.Items[I]).SourceFile;
-            UnitIR := UnitIR + '|' + UnitName + ':' + CacheKeyForFile(UnitPath);
-          end;
-
-        IRFile := IncludeTrailingPathDelimiter(CacheDir) + '__full__.ssa';
-        Source := TStringList.Create;
-        try
-          if FileExists(IRFile) and FileExists(IRFile + '.key') then
-          begin
-            Source.LoadFromFile(IRFile + '.key');
-            if Trim(Source.Text) = UnitIR then
-            begin
-              Source.LoadFromFile(IRFile);
-              IR := Source.Text;
-            end;
-          end;
-        finally
-          Source.Free;
-          Source := nil;
-        end;
-      end;
-      {$ENDIF}
-
-      { Full codegen (or fallback if caching was skipped/missed) }
-      if IR = '' then
-      begin
-        CG := TCodeGenQBE.Create;
-        try
-          if (Units <> nil) and (Units.Count > 0) then
-          begin
-            CG.SetSymbolTable(Prog.SymbolTable);
-            for I := 0 to Units.Count - 1 do
-              CG.AppendUnit(TUnit(Units.Items[I]));
-            CG.AppendProgram(Prog);
-          end
-          else
-            CG.Generate(Prog);
-          IR := CG.GetOutput;
-        finally
-          CG.Free;
-          CG := nil;
-        end;
-
-        {$IFDEF FPC}
-        if CacheDir <> '' then
+      CG := TCodeGenQBE.Create;
+      try
+        if (Units <> nil) and (Units.Count > 0) then
         begin
-          if ForceDirectories(CacheDir) then
-          begin
-            IRFile := IncludeTrailingPathDelimiter(CacheDir) + '__full__.ssa';
-            Source := TStringList.Create;
-            try
-              Source.Text := IR;
-              Source.SaveToFile(IRFile);
-            finally
-              Source.Free;
-              Source := nil;
-            end;
-            Source := TStringList.Create;
-            try
-              Source.Text := UnitIR;
-              Source.SaveToFile(IRFile + '.key');
-            finally
-              Source.Free;
-              Source := nil;
-            end;
-          end;
-        end;
-        {$ENDIF}
+          CG.SetSymbolTable(Prog.SymbolTable);
+          for I := 0 to Units.Count - 1 do
+            CG.AppendUnit(TUnit(Units.Items[I]));
+          CG.AppendProgram(Prog);
+        end
+        else
+          CG.Generate(Prog);
+        IR := CG.GetOutput;
+      finally
+        CG.Free;
+        CG := nil;
       end;
 
       if OPDFEnabled then