feat(joinir): Phase 77 - BindingId expansion implementation (dev-only)

Phase 77 implements promoted_bindings population in DigitPos/Trim promoters
and deprecates legacy name-based resolution paths.

Changes:
- DigitPosPromoter: Added binding_map field and record_promoted_binding() calls
- TrimLoopHelper: Added binding_map field for ch → is_ch_match tracking
- Pattern2/4: Wired binding_map from builder.binding_map to promoters
- Legacy deprecation: Added #[deprecated] to resolve_promoted_join_id()
- Dual-path design: BindingId priority + name fallback maintained

Files modified (8):
- pattern2_with_break.rs, pattern4_with_continue.rs: binding_map wiring
- trim_loop_lowering.rs: Trim promoter integration
- carrier_info.rs: Deprecation warnings
- scope_manager.rs: Deprecated fallback paths
- loop_body_carrier_promoter.rs: Trim binding_map support
- loop_body_cond_promoter.rs: Orchestrator updates
- loop_body_digitpos_promoter.rs: DigitPos binding_map support

Tests: 958/958 PASS (zero regressions)
Design: Type-safe BindingId mapping replaces string-based promoted variable resolution

Phase 78+ will delete deprecated code (~50 lines) and make binding_map required.

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

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

src/mir/join_ir/lowering/scope_manager.rs

@@ -290,6 +290,13 @@ impl<'a> ScopeManager for Pattern2ScopeManager<'a> {
             }
 
             // Step 3: Fallback to legacy name-based lookup (Phase 75 fallback path)
+            // Phase 77: DEPRECATED - Will be removed in Phase 78+
+            #[cfg(feature = "normalized_dev")]
+            eprintln!(
+                "[phase77/fallback] WARNING: BindingId({}) for '{}' not resolved, falling back to name-based lookup (DEPRECATED)",
+                bid.0, name
+            );
+            #[cfg(not(feature = "normalized_dev"))]
             if std::env::var("NYASH_JOINIR_DEBUG").is_ok() {
                 eprintln!(
                     "[phase76/fallback] BindingId({}) miss, falling back to name '{}' lookup",
@@ -298,7 +305,8 @@ impl<'a> ScopeManager for Pattern2ScopeManager<'a> {
             }
         }
 
-        // Step 4: Legacy name-based lookup (Phase 75 behavior, will be removed in Phase 77)
+        // Step 4: Legacy name-based lookup (Phase 75 behavior)
+        // Phase 77: DEPRECATED - Will be removed in Phase 78+ after all call sites use BindingId
         self.lookup(name)
     }
 }