feat: Phase 8.2, 8.4, 8.5, 9.1 + C backend fixes

Phase 8.2 — Gradual Ownership:
- Add tkRef/tkMutRef types and `mut` keyword
- Add @[Checked] attribute for opt-in borrow checking
- Reject assignment through &T in checked functions
- examples/ownership.bux

Phase 8.4 — CTFE:
- Evaluate const func at compile-time via evalExpr/evalBlock
- Fold const declarations to literals; emit #define in C
- examples/ctfe.bux (Factorial(10) → 3628800)

Phase 8.5 — Trait Bounds:
- Change declFuncTypeParams from seq[string] to seq[TypeParam] (name + bound)
- Parser handles <T: Comparable>
- Sema checks typeImplements at call sites
- Fix C backend: generic receivers + pointer self field access
- examples/trait_bounds.bux

Phase 9.1 — Package Manager:
- Inline tables/arrays in TOML parser
- bux add, bux install, bux.lock generation
- Dependency resolution with git/path sources
- Build pipeline merges dependency .bux sources

C Backend Fixes:
- resolveExprType(ekIdent) now applies typeSubst for generic params
- Method desugaring works for monomorphized generic receivers
- Pointer checks use isPointer (covers tkRef/tkMutRef)
- Field access on &T emits -> instead of .

Remove accidentally committed test binaries from tracking

Makefile

@@ -3,7 +3,7 @@ SRC := src/main.nim
 OUT := buxc
 BUILD_DIR := build
 
-EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics generics_struct generic_infer generic_infer2 extend_generic pattern_matching strings strings2 map result_option try_operator
+EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics generics_struct generic_infer generic_infer2 extend_generic pattern_matching strings strings2 map result_option try_operator ownership ctfe
 
 .PHONY: all build dev test clean test-examples