refactor(joinir): Phase 287 P1 - Modularize ast_feature_extractor (facade pattern)

Extracted pattern recognizers from ast_feature_extractor.rs (1,148 lines) into
specialized modules under pattern_recognizers/ directory.

**Structure**:
- ast_feature_extractor.rs: Facade (135 lines, re-exports)
- pattern_recognizers/: 8 modules (1,126 lines total)
  - continue_break.rs: continue/break/return detection
  - infinite_loop.rs: loop(true) detection
  - if_else_phi.rs: if-else PHI pattern detection
  - carrier_count.rs: carrier variable counting
  - parse_number.rs: parse_number pattern (+ read_digits)
  - parse_string.rs: parse_string pattern (+ continue pattern)
  - skip_whitespace.rs: skip_whitespace pattern

**Contract**:
- Semantic invariance: All existing APIs preserved via re-exports
- No routing changes, no detection spec changes
- Public API unchanged (facade pattern)

**Verification**:
- Build: 0 errors, 0 warnings
- Pattern6: RC:9 (maintained)
- Smoke tests: 154/154 PASS

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

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

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

@@ -54,6 +54,7 @@
 
 pub(in crate::mir::builder) mod common; // Phase 255 P2: Common AST helpers
 pub(in crate::mir::builder) mod extractors; // Phase 282 P3: Common extraction interfaces
+pub(in crate::mir::builder) mod pattern_recognizers; // Phase 287 P1: Modularized pattern recognizers
 pub(in crate::mir::builder) mod ast_feature_extractor;
 pub(in crate::mir::builder) mod policies; // Phase 93/94: Pattern routing policies (future expansion)
 pub(in crate::mir::builder) mod body_local_policy; // Phase 92 P3: promotion vs slot routing