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

src/mir/builder/control_flow/joinir/patterns/router.rs

@@ -44,12 +44,15 @@ pub struct LoopPatternContext<'a> {
     pub debug: bool,
 
     /// Has continue statement(s) in body? (Phase 194+)
+    #[allow(dead_code)]
     pub has_continue: bool,
 
     /// Has break statement(s) in body? (Phase 194+)
+    #[allow(dead_code)]
     pub has_break: bool,
 
     /// Phase 192: Loop features extracted from AST
+    #[allow(dead_code)]
     pub features: LoopFeatures,
 
     /// Phase 192: Pattern classification based on features
@@ -119,6 +122,7 @@ pub struct LoopPatternEntry {
     pub name: &'static str,
 
     /// Priority (lower = tried first). Pattern1=10, Pattern2=20, Pattern3=30
+    #[allow(dead_code)]
     pub priority: u8,
 
     /// Detection function: returns true if this pattern matches