feat: complete OpenClaw plugin migration with SQLite persistence

- Migrate to OpenClaw Plugin SDK with definePluginEntry and api.registerTool
- Rewrite GraphDatabase with better-sqlite3 for persistent storage
- Implement recall depth traversal, timeRange filtering, supersede mode
- Add archive and cleanup data management features
- Fix SKILL.md frontmatter to OpenClaw single-line format (kebab-case names)
- Add ToolLimiter for per-turn rate limiting
- Add TypeBox parameter schemas for OpenClaw tool registration
- Add 110 tests across 4 test files (GraphDatabase, MemoryService, Tool, Limiter)
- Update README for OpenClaw plugin installation and usage

ts/openclaw.plugin.json

@@ -0,0 +1,15 @@
+{
+  "id": "graph-memory",
+  "name": "Graph Memory",
+  "description": "让 AI 拥有真正的长期记忆能力 - 基于图数据库的记忆系统",
+  "configSchema": {
+    "type": "object",
+    "additionalProperties": false,
+    "properties": {
+      "dbPath": {
+        "type": "string",
+        "description": "SQLite 数据库文件路径，默认 graph_memory.db"
+      }
+    }
+  }
+}