feat(joinir): Phase 52-53 LoopFrontendBinding JSON + Statement Handlers

Phase 52: LoopFrontendBinding JSON generation fixes
- Add receiver_to_json() for Field node structure (me.tokens)
- Add needs_me_receiver() for instance method detection
- Fix "condition" → "cond" key for JoinIR Frontend
- Add me parameter propagation in loop_patterns.rs
- Add JoinIR-compatible type fields in ast_json.rs
  - Variable → "type": "Var"
  - Literal → "type": "Int"/"Bool" (literal_to_joinir_json)
  - BinaryOp → "type": "Binary"/"Compare" (is_compare_op)
  - MethodCall → "type": "Method"

Phase 53: Statement Handler module for loop body
- NEW: stmt_handlers.rs with StatementEffect type
- Support: Local, Assignment, Print, Method, If statements
- If lowering: single variable update → Select instruction
- Remove hardcoded assert in loop_patterns.rs
- Replace with generic lower_statement() calls

Test results: 56 JoinIR tests PASS, 7 loop_frontend_binding tests PASS

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

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

src/mir/builder/control_flow.rs

@@ -173,6 +173,17 @@ impl super::MirBuilder {
         // Phase 50: Generate Local declarations from binding
         let (i_local, acc_local, n_local) = binding.generate_local_declarations();
 
+        // Phase 52: Check if `me` receiver is needed
+        // Instance methods (like print_tokens) need `me` to be passed as a parameter
+        let params: Vec<serde_json::Value> = if binding.needs_me_receiver() {
+            if debug {
+                eprintln!("[cf_loop/joinir] Adding 'me' to params (instance method)");
+            }
+            vec![serde_json::json!("me")]
+        } else {
+            vec![]
+        };
+
         // Step 2: Construct JSON v0 format with "defs" array
         // The function is named "simple" to match JoinIR Frontend's pattern matching
         // Phase 50: Include i/acc/n Local declarations to satisfy JoinIR Frontend expectations
@@ -180,7 +191,7 @@ impl super::MirBuilder {
             "defs": [
                 {
                     "name": "simple",
-                    "params": [],
+                    "params": params,
                     "body": {
                         "type": "Block",
                         "body": [
@@ -190,7 +201,7 @@ impl super::MirBuilder {
                             n_local,
                             {
                                 "type": "Loop",
-                                "condition": condition_json,
+                                "cond": condition_json,  // JoinIR Frontend expects "cond" not "condition"
                                 "body": body_json
                             },
                             // Return the accumulator (or null for side-effect loops)