Fix TProgram.Uses reserved-word clash (renamed to UsedUnits), nested
brace-comment in uParser.pas, and missing uAST in Blaise.pas uses clause.
Vendor QBE 1.2 source in vendor/qbe/ (built locally with make; binary
excluded via .gitignore). End-to-end pipeline confirmed: Blaise compiles
Hello World and Calc (6*7=42) to native x86_64 Linux binaries.
71/71 FPCUnit tests passing.
