refactor(joinir): Phase 79 - Detector/Recorder separation + BindingMapProvider

**Phase 79 Medium-Priority Refactoring Complete**

## Action 1: Detector/Recorder Separation

**New Pure Detection Logic:**
- `digitpos_detector.rs` (~350 lines, 7 tests)
  - Pure detection for A-4 DigitPos pattern
  - No binding_map dependency
  - Independently testable

- `trim_detector.rs` (~410 lines, 9 tests)
  - Pure detection for A-3 Trim pattern
  - No binding_map dependency
  - Comprehensive test coverage

**Simplified Promoters:**
- `DigitPosPromoter`: 200+ → 80 lines (60% reduction)
  - Uses DigitPosDetector for detection
  - Focuses on orchestration + recording
  - Removed 6 helper methods

- `LoopBodyCarrierPromoter`: 160+ → 70 lines (56% reduction)
  - Uses TrimDetector for detection
  - Clean separation of concerns
  - Removed 3 helper methods

## Action 2: BindingMapProvider Trait

**Centralized Feature Gate:**
- `binding_map_provider.rs` (~100 lines, 3 tests)
  - Trait to abstract binding_map access
  - #[cfg] guards: 10+ locations → 2 locations (80% reduction)

- `MirBuilder` implementation
  - Clean feature-gated access
  - Single point of control

## Quality Metrics

**Code Reduction:**
- DigitPosPromoter: 200+ → 80 lines (60%)
- LoopBodyCarrierPromoter: 160+ → 70 lines (56%)
- Feature guards: 10+ → 2 locations (80%)

**Tests:**
- All tests passing: 970/970 (100%)
- New test coverage: 19+ tests for detectors
- No regressions

**Design Improvements:**
- ✅ Single Responsibility Principle
- ✅ Independent unit testing
- ✅ Reusable detection logic
- ✅ Centralized feature gating

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

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

src/mir/builder.rs

@@ -1108,6 +1108,22 @@ impl Default for MirBuilder {
     }
 }
 
+// Phase 79: BindingMapProvider implementation
+// Centralizes feature-gated binding_map access for promoters
+use crate::mir::loop_pattern_detection::BindingMapProvider;
+
+impl BindingMapProvider for MirBuilder {
+    #[cfg(feature = "normalized_dev")]
+    fn get_binding_map(&self) -> Option<&std::collections::BTreeMap<String, crate::mir::BindingId>> {
+        Some(&self.binding_map)
+    }
+
+    #[cfg(not(feature = "normalized_dev"))]
+    fn get_binding_map(&self) -> Option<&std::collections::BTreeMap<String, crate::mir::BindingId>> {
+        None
+    }
+}
+
 #[cfg(test)]
 mod binding_id_tests {
     use super::*;