Remove legacy redundant code after Gatekeeper Box consolidation

Summary of Deletions:
- Remove core/box/unified_batch_box.c (26 lines)
  * Legacy batch allocation logic superseded by Alloc Gatekeeper Box
  * unified_cache now handles allocation aggregation

- Remove core/box/unified_batch_box.h (29 lines)
  * Header declarations for deprecated unified_batch_box module

- Remove core/tiny_free_fast.inc.h (329 lines)
  * Legacy fast-path free implementation
  * Functionality consolidated into:
    - tiny_free_gate_box.h (Fail-Fast layer + diagnostics)
    - malloc_tiny_fast.h (Free path integration)
    - unified_cache (return to freelist)
  * Code path now routes through Gatekeeper Box for consistency

Build System Updates:
- Update Makefile
  * Remove unified_batch_box.o from OBJS_BASE
  * Remove unified_batch_box_shared.o from SHARED_OBJS
  * Remove unified_batch_box.o from BENCH_HAKMEM_OBJS_BASE

- Update core/hakmem_tiny_phase6_wrappers_box.inc
  * Remove unified_batch_box references
  * Simplify allocation wrapper to use new Gatekeeper architecture

Impact:
- Removes ~385 lines of redundant/superseded code
- Consolidates allocation logic through unified Gatekeeper entry points
- All functionality preserved via new Box-based architecture
- Simplifies codebase and reduces maintenance burden

Testing:
- Build verification: make clean && make RELEASE=0/1
- Smoke tests: All pass (simple_alloc, loop 10M, pool_tls)
- No functional regressions

Rationale:
After implementing Alloc/Free Gatekeeper Boxes with Fail-Fast layers
and Unified Cache type safety, the legacy separate implementations
became redundant. This commit completes the architectural consolidation
and simplifies the allocator codebase.

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

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

core/box/front_gate_classifier.d

@@ -19,7 +19,8 @@ core/box/front_gate_classifier.o: core/box/front_gate_classifier.c \
  core/box/../hakmem_build_flags.h core/box/../hakmem_internal.h \
  core/box/../hakmem.h core/box/../hakmem_config.h \
  core/box/../hakmem_features.h core/box/../hakmem_sys.h \
- core/box/../hakmem_whale.h core/box/../hakmem_tiny_config.h
+ core/box/../hakmem_whale.h core/box/../hakmem_tiny_config.h \
+ core/box/../pool_tls_registry.h
 core/box/front_gate_classifier.h:
 core/box/../tiny_region_id.h:
 core/box/../hakmem_build_flags.h:
@@ -54,3 +55,4 @@ core/box/../hakmem_features.h:
 core/box/../hakmem_sys.h:
 core/box/../hakmem_whale.h:
 core/box/../hakmem_tiny_config.h:
+core/box/../pool_tls_registry.h: