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/trait_bounds.bux

@@ -0,0 +1,28 @@
+import Std::Io::{PrintLine, PrintInt};
+
+// Trait (interface) definition
+interface Drawable {
+    func Draw(self: &Self);
+}
+
+// Type that implements the trait
+struct Circle {
+    radius: int;
+}
+
+extend Circle for Drawable {
+    func Draw(self: &Circle) {
+        PrintLine("Drawing circle");
+    }
+}
+
+// Generic function with trait bound: T must implement Drawable
+func Render<T: Drawable>(obj: T) {
+    obj.Draw();
+}
+
+func Main() -> int {
+    let c: Circle = Circle { radius: 5 };
+    Render(c);  // OK: Circle implements Drawable
+    return 0;
+}