Add schema migration

src/schema.ts

@@ -0,0 +1,20 @@
+export const SCHEMA_MIGRATION = `
+CREATE TABLE IF NOT EXISTS memories_v2 (
+  id TEXT PRIMARY KEY,
+  text TEXT NOT NULL,
+  embedding BLOB NOT NULL,
+  type TEXT NOT NULL DEFAULT 'semantic' CHECK (type IN ('episodic', 'semantic', 'procedural')),
+  source TEXT NOT NULL DEFAULT 'user' CHECK (source IN ('user', 'assistant')),
+  created_at INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000),
+  last_accessed_at INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000),
+  access_count INTEGER NOT NULL DEFAULT 0,
+  importance REAL NOT NULL DEFAULT 0.5 CHECK (importance >= 0 AND importance <= 1),
+  conversation_id TEXT,
+  metadata TEXT
+);
+CREATE INDEX IF NOT EXISTS idx_memories_type ON memories_v2(type);
+CREATE INDEX IF NOT EXISTS idx_memories_source ON memories_v2(source);
+CREATE INDEX IF NOT EXISTS idx_memories_created ON memories_v2(created_at DESC);
+CREATE INDEX IF NOT EXISTS idx_memories_accessed ON memories_v2(last_accessed_at DESC);
+CREATE INDEX IF NOT EXISTS idx_memories_importance ON memories_v2(importance DESC);
+`;