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>

lang/src/runner/stage1_cli.hako

@@ -327,10 +327,12 @@ static box Stage1Cli {
     }
     local prog_path = null
     local source_path = null
+    // Predeclare to avoid creating loop-body-local variables in the condition scope.
+    local arg = ""
 
     local i = 2
     loop(i < argc) {
-      local arg = "" + args.get(i)
+      arg = "" + args.get(i)
       if arg == "--from-program-json" {
         if i + 1 >= argc {
           print("[stage1-cli] emit mir-json: --from-program-json requires a path")
@@ -392,10 +394,12 @@ static box Stage1Cli {
     }
     local backend = "vm"
     local source_path = null
+    // Predeclare to keep the loop condition independent of loop-body-local variables.
+    local arg = ""
 
     local i = 1
     loop(i < argc) {
-      local arg = "" + args.get(i)
+      arg = "" + args.get(i)
       if arg == "--backend" {
         if i + 1 >= argc {
           print("[stage1-cli] run: --backend requires a value (vm|llvm|pyvm)")
@@ -403,11 +407,13 @@ static box Stage1Cli {
         }
         backend = "" + args.get(i + 1)
         i = i + 2
-      } else {
-        source_path = arg
-        i = i + 1
-        break
+        continue
       }
+
+      // First non-option argument is the source path; exit loop after capture.
+      source_path = arg
+      i = i + 1
+      if source_path != null { i = argc }
     }
 
     if source_path == null || source_path == "" {