feat(joinir): Phase 245C - Function parameter capture + test fix

Extend CapturedEnv to include function parameters used in loop conditions,
enabling ExprLowerer to resolve variables like `s` in `loop(p < s.length())`.

Phase 245C changes:
- function_scope_capture.rs: Add collect_names_in_loop_parts() helper
- function_scope_capture.rs: Extend analyze_captured_vars_v2() with param capture logic
- function_scope_capture.rs: Add 4 new comprehensive tests

Test fix:
- expr_lowerer/ast_support.rs: Accept all MethodCall nodes for syntax support
  (validation happens during lowering in MethodCallLowerer)

Problem solved: "Variable not found: s" errors in loop conditions

Test results: 924/924 PASS (+13 from baseline 911)

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

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

src/mir/join_ir/lowering/loop_view_builder.rs

@@ -76,7 +76,7 @@ impl LoopViewBuilder {
 
         // Phase 170-A-2: Structure-based routing with CaseALoweringShape
         let carrier_names: Vec<String> = scope.carriers.iter().cloned().collect();
-        let update_summary = loop_update_summary::analyze_loop_updates(&carrier_names);
+        let update_summary = loop_update_summary::analyze_loop_updates_by_name(&carrier_names);
 
         let stub_features = crate::mir::loop_pattern_detection::LoopFeatures {
             has_break: false,