Box API Phase 1-3: Capacity Manager, Carve-Push, Prewarm 実装

Priority 1-3のBox Modulesを実装し、安全なpre-warming APIを提供。
既存の複雑なprewarmコードを1行のBox API呼び出しに置き換え。

## 新規Box Modules

1. **Box Capacity Manager** (capacity_box.h/c)
   - TLS SLL容量の一元管理
   - adaptive_sizing初期化保証
   - Double-free バグ防止

2. **Box Carve-And-Push** (carve_push_box.h/c)
   - アトミックなblock carve + TLS SLL push
   - All-or-nothing semantics
   - Rollback保証（partial failure防止）

3. **Box Prewarm** (prewarm_box.h/c)
   - 安全なTLS cache pre-warming
   - 初期化依存性を隠蔽
   - シンプルなAPI (1関数呼び出し)

## コード簡略化

hakmem_tiny_init.inc: 20行 → 1行
```c
// BEFORE: 複雑なP0分岐とエラー処理
adaptive_sizing_init();
if (prewarm > 0) {
    #if HAKMEM_TINY_P0_BATCH_REFILL
        int taken = sll_refill_batch_from_ss(5, prewarm);
    #else
        int taken = sll_refill_small_from_ss(5, prewarm);
    #endif
}

// AFTER: Box API 1行
int taken = box_prewarm_tls(5, prewarm);
```

## シンボルExport修正

hakmem_tiny.c: 5つのシンボルをstatic → non-static
- g_tls_slabs[] (TLS slab配列)
- g_sll_multiplier (SLL容量乗数)
- g_sll_cap_override[] (容量オーバーライド)
- superslab_refill() (SuperSlab再充填)
- ss_active_add() (アクティブカウンタ)

## ビルドシステム

Makefile: TINY_BENCH_OBJS_BASEに3つのBox modules追加
- core/box/capacity_box.o
- core/box/carve_push_box.o
- core/box/prewarm_box.o

## 動作確認

✅ Debug build成功
✅ Box Prewarm API動作確認
   [PREWARM] class=5 requested=128 taken=32

## 次のステップ

- Box Refill Manager (Priority 4)
- Box SuperSlab Allocator (Priority 5)
- Release build修正（tiny_debug_ring_record）

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

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

core/box/capacity_box.h

@@ -0,0 +1,52 @@
+// capacity_box.h - Box Capacity Manager
+// Priority 1 Box: TLS Cache Capacity Management
+//
+// Purpose:
+//   - Centralize all capacity calculations (adaptive sizing, SLL cap, etc.)
+//   - Prevent initialization order bugs (root cause of prewarm double-free)
+//   - Provide simple, safe API for capacity queries
+//
+// Design:
+//   - Wraps adaptive_sizing system
+//   - Idempotent initialization
+//   - Bounds checking built-in
+//   - Thread-safe (uses TLS)
+
+#ifndef HAKMEM_BOX_CAPACITY_H
+#define HAKMEM_BOX_CAPACITY_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+// ============================================================================
+// Box Capacity API
+// ============================================================================
+
+// Initialize capacity system (idempotent - safe to call multiple times)
+// MUST be called before any other box_cap_* functions
+void box_cap_init(void);
+
+// Get current TLS SLL capacity for a class
+// Returns: capacity in blocks, or 0 if not initialized
+// Thread-safe: uses TLS
+uint32_t box_cap_get(int class_idx);
+
+// Check if TLS SLL has room for N blocks
+// Returns: true if N blocks can be added, false otherwise
+// Thread-safe: uses TLS
+bool box_cap_has_room(int class_idx, uint32_t n);
+
+// Get available space in TLS SLL
+// Returns: number of blocks that can be added
+// Thread-safe: uses TLS
+uint32_t box_cap_avail(int class_idx);
+
+// Update capacity (adaptive sizing hook)
+// Note: Normally called by adaptive sizing system, not manually
+void box_cap_update(int class_idx, uint32_t new_cap);
+
+// Check if capacity system is initialized
+// Returns: true if box_cap_init() was called
+bool box_cap_is_initialized(void);
+
+#endif // HAKMEM_BOX_CAPACITY_H