feat(joinir): Phase 75 - BindingId pilot lookup (dev-only)

Phase 75 pilots BindingId-based variable lookup in the ScopeManager and
ConditionEnv components. Demonstrates "BindingId priority → name fallback"
strategy with comprehensive testing and zero production impact.

Changes:
- scope_manager.rs: Added lookup_with_binding() trait method
- condition_env.rs: Implemented resolve_var_with_binding() with 3-tier fallback
- expr_lowerer.rs: Integrated pilot lookup paths
- condition_lowering_box.rs: Updated with BindingId support

Tests: 3/3 new pilot tests PASS (priority/fallback/legacy)
Tests: lib 958/958 PASS, normalized_dev 54/54 PASS (no regressions)

Design: Feature-gated with normalized_dev, enables Phase 76 expansion.

🤖 Generated with Claude Code

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

src/mir/join_ir/lowering/expr_lowerer.rs

@@ -312,6 +312,8 @@ mod tests {
             carriers: vec![],
             trim_helper: None,
             promoted_loopbodylocals: vec![],
+#[cfg(feature = "normalized_dev")]
+            promoted_bindings: std::collections::BTreeMap::new(),
         };
 
         let scope = Pattern2ScopeManager {
@@ -356,6 +358,8 @@ mod tests {
             carriers: vec![],
             trim_helper: None,
             promoted_loopbodylocals: vec![],
+#[cfg(feature = "normalized_dev")]
+            promoted_bindings: std::collections::BTreeMap::new(),
         };
 
         let scope = Pattern2ScopeManager {
@@ -400,6 +404,8 @@ mod tests {
             carriers: vec![],
             trim_helper: None,
             promoted_loopbodylocals: vec![],
+#[cfg(feature = "normalized_dev")]
+            promoted_bindings: std::collections::BTreeMap::new(),
         };
 
         let scope = Pattern2ScopeManager {
@@ -480,6 +486,8 @@ mod tests {
             carriers: vec![],
             trim_helper: None,
             promoted_loopbodylocals: vec![],
+#[cfg(feature = "normalized_dev")]
+            promoted_bindings: std::collections::BTreeMap::new(),
         };
         let boxed_carrier: Box<CarrierInfo> = Box::new(carrier_info);
         let carrier_ref: &'static CarrierInfo = Box::leak(boxed_carrier);
@@ -507,6 +515,8 @@ mod tests {
             carriers: vec![],
             trim_helper: None,
             promoted_loopbodylocals: vec![],
+#[cfg(feature = "normalized_dev")]
+            promoted_bindings: std::collections::BTreeMap::new(),
         };
         let boxed_carrier: Box<CarrierInfo> = Box::new(carrier_info);
         let carrier_ref: &'static CarrierInfo = Box::leak(boxed_carrier);
@@ -656,6 +666,8 @@ mod tests {
             carriers: vec![],
             trim_helper: None,
             promoted_loopbodylocals: vec![],
+#[cfg(feature = "normalized_dev")]
+            promoted_bindings: std::collections::BTreeMap::new(),
         };
 
         let scope = Pattern2ScopeManager {