feat(parser): Phase 285A1.4 & A1.5 - Weak field sugar + Parser hang fix

A1.4: Add sugar syntax `public weak parent` ≡ `public { weak parent }`
A1.5: Fix parser hang on unsupported `param: Type` syntax

Key changes:
- A1.4: Extend visibility parser to handle weak modifier (fields.rs)
- A1.5: Shared helper `parse_param_name_list()` with progress-zero detection
- A1.5: Fix 6 vulnerable parameter parsing loops (methods, constructors, functions)
- Tests: Sugar syntax (OK/NG), parser hang (timeout-based)
- Docs: lifecycle.md, EBNF.md, phase-285a1-boxification.md

Additional changes:
- weak() builtin implementation (handlers/weak.rs)
- Leak tracking improvements (leak_tracker.rs)
- Documentation updates (lifecycle, types, memory-finalization, etc.)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/reference/testing-quality/golden-dump-testing.md

@@ -89,20 +89,21 @@ fn test_weak_reference_mir_stability() {
     let source = r#"
         box Parent { init { child_weak } }
         box Child { init { data } }
-        
+
         static box Main {
             main() {
                 local parent = new Parent()
                 local child = new Child(42)
                 parent.child_weak = weak(child)
-                
-                if parent.child_weak.isAlive() {
-                    print(parent.child_weak.get().data)
+
+                local c = parent.child_weak.weak_to_strong()
+                if c != null {
+                    print(c.data)
                 }
             }
         }
     "#;
-    
+
     verify_mir_golden("weak_reference", source);
 }
 ```
@@ -404,4 +405,4 @@ fi
 
 *最終更新: 2025-08-14 - ChatGPT5推奨3点セット完成*
 
-*Golden Dump Testing = Nyash品質保証の技術的基盤*
+*Golden Dump Testing = Nyash品質保証の技術的基盤*