Add SQLite storage foundation

Introduce a core-owned Kysely SQLite storage layer backed by
$WorkDir/db/rowboat.sqlite, with startup initialization, shutdown
cleanup, in-code migrations, and initial storage metadata schema.

Ignore database files in the workspace watcher, add focused
storage/watcher tests, and update Electron packaging to stage and rebuild
better-sqlite3 against Electron's native module ABI.

apps/x/packages/core/package.json

@@ -28,6 +28,7 @@
     "@x/shared": "workspace:*",
     "ai": "^5.0.133",
     "awilix": "^12.0.5",
+    "better-sqlite3": "^12.10.0",
     "chokidar": "^4.0.3",
     "cors": "^2.8.6",
     "cron-parser": "^5.5.0",
@@ -36,6 +37,7 @@
     "google-auth-library": "^10.5.0",
     "googleapis": "^169.0.0",
     "isomorphic-git": "^1.29.0",
+    "kysely": "^0.29.2",
     "mammoth": "^1.11.0",
     "node-html-markdown": "^2.0.0",
     "ollama-ai-provider-v2": "^1.5.4",
@@ -49,6 +51,7 @@
     "zod": "^4.2.1"
   },
   "devDependencies": {
+    "@types/better-sqlite3": "^7.6.13",
     "@types/cors": "^2.8.19",
     "@types/express": "^5.0.6",
     "@types/node": "^25.0.3",