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/loop_pattern_detection/mod.rs

@@ -196,7 +196,7 @@ impl LoopFeatures {
 ///
 /// # Returns
 /// * `LoopFeatures` - Feature vector for pattern classification
-pub fn extract_features(loop_form: &LoopForm, scope: Option<&LoopScopeShape>) -> LoopFeatures {
+pub(crate) fn extract_features(loop_form: &LoopForm, scope: Option<&LoopScopeShape>) -> LoopFeatures {
     // Phase 194: Basic feature extraction from LoopForm
     let has_break = !loop_form.break_targets.is_empty();
     let has_continue = !loop_form.continue_targets.is_empty();
@@ -611,7 +611,7 @@ pub fn is_loop_with_continue_pattern(loop_form: &LoopForm) -> bool {
 /// # TODO
 /// Implement by analyzing header PHI nodes
 #[allow(dead_code)]
-fn count_carrier_variables(loop_form: &LoopForm) -> usize {
+fn count_carrier_variables(_loop_form: &LoopForm) -> usize {
     // TODO: Implement carrier variable counting
     // Step 1: Access loop_form.header block
     // Step 2: Count PHI instructions in header
@@ -630,7 +630,7 @@ fn count_carrier_variables(loop_form: &LoopForm) -> usize {
 /// # TODO
 /// Implement by checking for LoopForm within body blocks
 #[allow(dead_code)]
-fn has_nested_loops(loop_form: &LoopForm) -> bool {
+fn has_nested_loops(_loop_form: &LoopForm) -> bool {
     // TODO: Implement nested loop detection
     // Step 1: Traverse body blocks
     // Step 2: Check for loop headers in body
@@ -649,7 +649,7 @@ fn has_nested_loops(loop_form: &LoopForm) -> bool {
 /// # TODO
 /// Implement by checking header condition complexity
 #[allow(dead_code)]
-fn has_simple_condition(loop_form: &LoopForm) -> bool {
+fn has_simple_condition(_loop_form: &LoopForm) -> bool {
     // TODO: Implement condition complexity check
     // Step 1: Access loop_form.header block
     // Step 2: Find condition instruction
@@ -660,7 +660,7 @@ fn has_simple_condition(loop_form: &LoopForm) -> bool {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    
 
     // ========================================================================
     // Pattern 1: Simple While Loop Tests