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/condition_pattern.rs

@@ -397,6 +397,15 @@ mod tests {
         assert!(is_simple_comparison(&cond));
     }
 
+    #[test]
+    fn pattern3_cond_i_mod_2_eq_1_is_recognized() {
+        // Pattern3/4 で使う典型的なフィルタ条件: i % 2 == 1
+        let lhs = binop(BinaryOperator::Modulo, var("i"), int_lit(2));
+        let cond = binop(BinaryOperator::Equal, lhs, int_lit(1));
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::SimpleComparison);
+        assert!(is_simple_comparison(&cond));
+    }
+
     #[test]
     fn test_complex_logical_and() {
         // a && b (logical And)
@@ -427,6 +436,19 @@ mod tests {
         assert!(!is_simple_comparison(&cond));
     }
 
+    #[test]
+    fn unsupported_nested_mod_condition_is_rejected() {
+        // (i % 2 == 1) && (j > 0) → 複合条件として Complex 扱い
+        let mod_eq = {
+            let lhs = binop(BinaryOperator::Modulo, var("i"), int_lit(2));
+            binop(BinaryOperator::Equal, lhs, int_lit(1))
+        };
+        let gt_zero = binop(BinaryOperator::Greater, var("j"), int_lit(0));
+        let cond = binop(BinaryOperator::And, mod_eq, gt_zero);
+        assert_eq!(analyze_condition_pattern(&cond), ConditionPattern::Complex);
+        assert!(!is_simple_comparison(&cond));
+    }
+
     #[test]
     fn test_complex_non_binary_op() {
         // Just a variable (not a comparison)