feat(joinir): Phase 224-B - MethodCallLowerer + CoreMethodId extension

- Extend CoreMethodId with is_pure(), allowed_in_condition(), allowed_in_init()
- New MethodCallLowerer box for metadata-driven MethodCall lowering
- Integrate MethodCall handling in condition_lowerer
- P0: Zero-argument methods (length) supported
- Design principle: NO method name hardcoding, CoreMethodId metadata only

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

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

src/mir/join_ir/lowering/mod.rs

@@ -30,6 +30,7 @@ pub mod loop_body_local_env; // Phase 184: Body-local variable environment
 pub mod loop_body_local_init; // Phase 186: Body-local init expression lowering
 pub(crate) mod condition_lowerer; // Phase 171-fix: Core condition lowering logic
 pub mod condition_to_joinir; // Phase 169: JoinIR condition lowering orchestrator (refactored)
+pub mod method_call_lowerer; // Phase 224-B: MethodCall lowering (metadata-driven)
 pub(crate) mod condition_var_extractor; // Phase 171-fix: Variable extraction from condition AST
 pub mod continue_branch_normalizer; // Phase 33-19: Continue branch normalization for Pattern B
 pub mod loop_update_analyzer; // Phase 197: Update expression analyzer for carrier semantics