feat(hako_check): Phase 153 - Dead code detection revival (JoinIR version)

Implement comprehensive dead code detection for hako_check with JoinIR
integration, following Phase 133/134/152 box-based modularity pattern.

## Key Achievements

1. **Comprehensive Inventory** (`phase153_hako_check_inventory.md`):
   - Documented current hako_check architecture (872 lines)
   - Analyzed existing HC011/HC012 rules
   - Confirmed JoinIR-only pipeline (Phase 124)
   - Identified Phase 153 opportunities

2. **DeadCodeAnalyzerBox** (`rule_dead_code.hako`):
   - Unified HC019 rule (570+ lines)
   - Method-level + box-level dead code detection
   - DFS reachability from entrypoints
   - Text-based analysis (no MIR JSON dependency for MVP)
   - Heuristic-based false positive reduction

3. **CLI Integration** (`cli.hako`):
   - Added `--dead-code` flag for comprehensive mode
   - Added `--rules dead_code` for selective execution
   - Compatible with --format (text/json-lsp/dot)

4. **Test Infrastructure**:
   - HC019_dead_code test directory (ng/ok/expected.json)
   - `hako_check_deadcode_smoke.sh` with 4 test cases

## Technical Details

- **Input**: Analysis IR (MapBox with methods/calls/boxes/entrypoints)
- **Output**: HC019 diagnostics
- **Algorithm**: Graph-based DFS reachability
- **Pattern**: Box-based modular architecture
- **No ENV vars**: CLI flags only

## Files Modified

- NEW: docs/development/current/main/phase153_hako_check_inventory.md
- NEW: tools/hako_check/rules/rule_dead_code.hako
- MOD: tools/hako_check/cli.hako
- NEW: tools/hako_check/tests/HC019_dead_code/
- NEW: tools/hako_check_deadcode_smoke.sh
- MOD: CURRENT_TASK.md

## Next Steps

- Phase 154+: MIR CFG integration for block-level detection
- Phase 160+: Integration with .hako JoinIR/MIR migration

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

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

tools/hako_check/cli.hako

@@ -17,6 +17,7 @@ using tools.hako_check.rules.rule_arity_mismatch as RuleArityMismatchBox
 using tools.hako_check.rules.rule_stage3_gate as RuleStage3GateBox
 using tools.hako_check.rules.rule_brace_heuristics as RuleBraceHeuristicsBox
 using tools.hako_check.rules.rule_analyzer_io_safety as RuleAnalyzerIoSafetyBox
+using tools.hako_check.rules.rule_dead_code as DeadCodeAnalyzerBox
 using tools.hako_check.render.graphviz as GraphvizRenderBox
 using tools.hako_parser.parser_core as HakoParserCoreBox
 
@@ -43,11 +44,13 @@ static box HakoAnalyzerBox {
     // optional filters
     local rules_only = null  // ArrayBox of keys
     local rules_skip = null  // ArrayBox of keys
+    local dead_code_mode = 0  // Phase 153: --dead-code flag
     // Support inline sources: --source-file <path> <text>. Also accept --debug and --format anywhere.
     while i < args.size() {
       local p = args.get(i)
       // handle options
       if p == "--debug" { debug = 1; i = i + 1; continue }
+      if p == "--dead-code" { dead_code_mode = 1; i = i + 1; continue }
       if p == "--no-ast" { no_ast = 1; i = i + 1; continue }
       if p == "--force-ast" { no_ast = 0; i = i + 1; continue }
       if p == "--format" {
@@ -219,6 +222,17 @@ static box HakoAnalyzerBox {
         local added = after_n - before_n
         print("[hako_check/HC015] file=" + p + " added=" + me._itoa(added) + " total_out=" + me._itoa(after_n))
       }
+      // Phase 153: HC019 Dead Code Analyzer (comprehensive)
+      before_n = out.size()
+      if dead_code_mode == 1 || me._rule_enabled(rules_only, rules_skip, "dead_code") == 1 {
+        me._log_stderr("[rule/exec] HC019 (dead_code) " + p)
+        DeadCodeAnalyzerBox.apply_ir(ir, p, out)
+      }
+      if debug == 1 {
+        local after_n = out.size()
+        local added = after_n - before_n
+        print("[hako_check/HC019] file=" + p + " added=" + me._itoa(added) + " total_out=" + me._itoa(after_n))
+      }
       // suppression: HC012(dead box) > HC011(unreachable method)
       local filtered = me._suppress_overlap(out)
       // flush (text only)
@@ -568,6 +582,7 @@ static box HakoAnalyzerBox {
         // Rules that need IR
         if k == "dead_methods" { return 1 }
         if k == "dead_static_box" { return 1 }
+        if k == "dead_code" { return 1 }
         if k == "duplicate_method" { return 1 }
         if k == "missing_entrypoint" { return 1 }
         if k == "arity_mismatch" { return 1 }