feat(joinir): Phase 183 LoopBodyLocal role separation + test fixes

Phase 183 Implementation:
- Added is_var_used_in_condition() helper for AST variable detection
- Implemented LoopBodyLocal filtering in TrimLoopLowerer
- Created 4 test files for P1/P2 patterns
- Added 5 unit tests for variable detection

Test Fixes:
- Fixed test_is_outer_scope_variable_pinned (BasicBlockId import)
- Fixed test_pattern2_accepts_loop_param_only (literal node usage)

Refactoring:
- Unified pattern detection documentation
- Consolidated CarrierInfo initialization
- Documented LoopScopeShape construction paths

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

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

src/mir/join_ir/lowering/loop_patterns/mod.rs

@@ -76,7 +76,7 @@ pub use with_continue::lower_loop_with_continue_to_joinir;
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    
 
     // ========================================================================
     // Pattern 1: Simple While Loop Tests

src/mir/join_ir/lowering/loop_patterns/simple_while.rs

@@ -90,8 +90,8 @@ use crate::mir::loop_form::LoopForm;
 /// }
 /// ```
 pub fn lower_simple_while_to_joinir(
-    loop_form: &LoopForm,
-    lowerer: &mut LoopToJoinLowerer,
+    _loop_form: &LoopForm,
+    _lowerer: &mut LoopToJoinLowerer,
 ) -> Option<JoinInst> {
     // TODO: Implement Pattern 1 lowering
     //