feat(server): per-key quota + response cache (v3.8.0) (#18)

Add two new features for LAN sharing governance:

Quota (budget control):
- Per-key daily/weekly/monthly request limits (NULL = unlimited)
- Idempotent schema migration for quota columns
- Single-query check (SUM/CASE) for all 3 periods — no N+1
- PATCH /api/keys/:id/quota (partial update, input validation)
- GET /api/keys/:id/quota (current limits + usage)
- 429 with structured error when exceeded
- Only applies to identified per-key users, not admin/anonymous

Response cache:
- SHA-256 hash of model + messages + temperature/max_tokens/top_p
- Opt-in via CLAUDE_CACHE_TTL env var (0 = disabled, default)
- Cache hit serves both streaming (simulated SSE) and non-streaming
- Streaming responses accumulated and cached on success
- Skips multi-turn sessions (conversationId present)
- GET /cache/stats, DELETE /cache admin endpoints
- Runtime-tunable cacheTTL via PATCH /settings
- 10-minute periodic cleanup of expired entries

Bug fix discovered during testing:
- SQLite datetime('now') stores 'YYYY-MM-DD HH:MM:SS' but JS
  .toISOString() produces 'YYYY-MM-DDTHH:MM:SS.sssZ'. String
  comparison breaks for same-day ranges. Added sqliteDatetime()
  helper for correct format matching.

Code review fixes:
- DELETE /api/keys/:id no longer shadows /quota sub-routes
- updateKeyQuota uses partial UPDATE (only SET provided fields)
- cacheHash includes temperature/max_tokens/top_p in hash
- Replaced raw getDb() in server.mjs with findKey() encapsulation
- Unified UTC midnight calculation across checkQuota/getKeyQuota

Includes 24-test integration suite (test-features.mjs).

Co-authored-by: Tao Deng <dtzp555@gmail.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "openclaw-claude-proxy",
-  "version": "3.7.0",
+  "version": "3.8.0",
   "description": "OCP (Open Claude Proxy) — use your Claude Pro/Max subscription as an OpenAI-compatible API for any IDE. Works with Cline, OpenCode, Aider, Continue.dev, OpenClaw, and more.",
   "type": "module",
   "bin": {