feat(joinir): Phase 213-2 Step 2-2 & 2-3 Data structure extensions

Extended PatternPipelineContext and CarrierUpdateInfo for Pattern 3 AST-based generalization.

Changes:
1. PatternPipelineContext:
   - Added loop_condition: Option<ASTNode>
   - Added loop_body: Option<Vec<ASTNode>>
   - Added loop_update_summary: Option<LoopUpdateSummary>
   - Updated build_pattern_context() for Pattern 3

2. CarrierUpdateInfo:
   - Added then_expr: Option<ASTNode>
   - Added else_expr: Option<ASTNode>
   - Updated analyze_loop_updates() with None defaults

Status: Phase 213-2 Steps 2-2 & 2-3 complete
Next: Create Pattern3IfAnalyzer to extract if statement and populate update summary

docs/guides/exception-handling.md

@@ -115,6 +115,6 @@ connect(url)
   cleanup { env.console.log("done") }
 
 // Stage‑3 parser gate quick smoke (direct acceptance)
-//   NYASH_PARSER_STAGE3=1 ./target/release/nyash --backend vm \
+//   NYASH_PARSER_STAGE3=1 ./target/release/hakorune --backend vm \
 //     apps/tests/macro/exception/expr_postfix_direct.hako
 ```