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

examples/ctfe.bux

@@ -0,0 +1,19 @@
+import Std::Io::PrintInt;
+
+// const func — evaluated at compile time
+const func Factorial(n: int) -> int {
+    if n <= 1 {
+        return 1;
+    }
+    return n * Factorial(n - 1);
+}
+
+// Compile-time constants
+const FIB_10 = Factorial(10);
+const SIMPLE = 5 + 3 * 2;
+
+func Main() -> int {
+    PrintInt(FIB_10);   // 3628800 — computed at compile time
+    PrintInt(SIMPLE);   // 11 — computed at compile time
+    return 0;
+}