feat(phase285w): Implement weak x unary operator syntax

Phase 285W-Syntax-0: Migrate weak reference syntax from function call
to unary operator for consistency and clarity.

**Changes**:
- Parser: Add UnaryOperator::Weak variant and parse_unary() handling
- MIR: Lower UnaryOp::Weak to emit_weak_new() (reuses existing path)
- AST: Add Weak to UnaryOperator enum + Display/JSON support
- Tests: Migrate 8 files from `weak(x)` to `weak x` syntax
  - 7 .hako test files updated
  - 1 smoke test shell script updated
- Cleanup: Remove obsolete weak(x) parser/MIR special cases
- Docs: Update Phase 285 README

**Syntax Change**:
- Old: `local w = weak(x)`  (function call)
- New: `local w = weak x`   (unary operator)

**Validation**: All migrated phase285* smoke tests pass (4/4 relevant)

**SSOT**: docs/reference/language/lifecycle.md

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

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

docs/development/current/main/phases/phase-285/README.md

@@ -10,8 +10,10 @@ Status: In progress (A1 series implemented; LLVM sub-phases ongoing)
 | 285LLVM-1.2 | ✅ COMPLETE | WeakRef基本動作（identity保留） (2025-12-24) |
 | 285LLVM-1.3 | ✅ COMPLETE | InstanceBox Field Access (getField/setField) (2025-12-24) |
 | **285LLVM-1.4** | ✅ **COMPLETE** | **print Handle Resolution (型タグ伝播)** (2025-12-24) |
+| **285W-Syntax-0** | ✅ **COMPLETE** | **weak文法SSOT確定 (weak x unary operator)** (2025-12-24) |
 
 **LLVM Details**: See [phase-285llvm-1.3-verification-report.md](phase-285llvm-1.3-verification-report.md)
+**Syntax Change**: Phase 285W-Syntax-0 migrates from `weak(x)` function call to `weak x` unary operator
 
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