feat(phase32): L-2.1 Stage-1 UsingResolver JoinIR integration + cleanup

Phase 32 L-2.1 complete implementation:

1. Stage-1 UsingResolver main line JoinIR connection
   - CFG-based LoopForm construction for resolve_for_source/5
   - LoopToJoinLowerer integration with handwritten fallback
   - JSON snapshot tests 6/6 PASS

2. JoinIR/VM Bridge improvements
   - Simplified join_ir_vm_bridge.rs dispatch logic
   - Enhanced json.rs serialization
   - PHI core boxes cleanup (local_scope_inspector, loop_exit_liveness, loop_var_classifier)

3. Stage-1 CLI enhancements
   - Extended args.rs, groups.rs, mod.rs for new options
   - Improved stage1_bridge module (args, env, mod)
   - Updated stage1_cli.hako

4. MIR builder cleanup
   - Simplified if_form.rs control flow
   - Removed dead code from loop_builder.rs
   - Enhanced phi_merge.rs

5. Runner module updates
   - json_v0_bridge/lowering.rs improvements
   - dispatch.rs, selfhost.rs, modes/vm.rs cleanup

6. Documentation updates
   - CURRENT_TASK.md, AGENTS.md
   - Various docs/ updates

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

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

src/mir/phi_core/local_scope_inspector.rs

@@ -168,7 +168,8 @@ impl LocalScopeInspectorBox {
     ///
     /// LoopScopeShape::classify() は既に exit_live 情報を含んでいるため、
     /// 直接 classify() → needs_exit_phi() を使う方が効率的。
-    pub fn is_available_in_all_with_scope(
+    #[allow(dead_code)] // Phase 30 F-1.3: will be used when LocalScopeInspectorBox is absorbed
+    pub(crate) fn is_available_in_all_with_scope(
         &self,
         var_name: &str,
         scope: &crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape,

src/mir/phi_core/loop_exit_liveness.rs

@@ -195,7 +195,8 @@ impl LoopExitLivenessBox {
     /// let scope = LoopScopeShape::from_existing_boxes(...)?;
     /// let live = liveness_box.get_exit_live_from_scope(&scope);
     /// ```
-    pub fn get_exit_live_from_scope(
+    #[allow(dead_code)] // Phase 30 F-1.2: will be used when LoopExitLivenessBox is absorbed
+    pub(crate) fn get_exit_live_from_scope(
         &self,
         scope: &crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape,
     ) -> BTreeSet<String> {

src/mir/phi_core/loop_var_classifier.rs

@@ -278,7 +278,8 @@ impl LoopVarClassBox {
     /// let scope = LoopScopeShape::from_existing_boxes(...)?;
     /// let class = classifier.classify_with_scope("ch", &scope);
     /// ```
-    pub fn classify_with_scope(
+    #[allow(dead_code)] // Phase 30 F-1.1: will be used when LoopVarClassBox is absorbed
+    pub(crate) fn classify_with_scope(
         &self,
         var_name: &str,
         scope: &crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape,
@@ -287,7 +288,8 @@ impl LoopVarClassBox {
     }
 
     /// Phase 30: LoopScopeShape を使って複数変数を一括分類
-    pub fn classify_all_with_scope(
+    #[allow(dead_code)] // Phase 30 F-1.1: will be used when LoopVarClassBox is absorbed
+    pub(crate) fn classify_all_with_scope(
         &self,
         var_names: &[String],
         scope: &crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape,