fix(db): point db:migrate at the live appliance DB by default

`db:migrate` (and drizzle-kit's config default) resolved DATABASE_URL to
`./parking.sqlite` relative to packages/db — a stray, half-empty leftover DB,
not the real store at apps/server/parking.sqlite. Running `pnpm --filter
@parking/db db:migrate` with no env therefore migrated the wrong file and
failed on its broken state, while the real DB went untouched.

Default DATABASE_URL to ../../apps/server/parking.sqlite in both the db:migrate
script and drizzle.config.ts (an explicit DATABASE_URL still overrides). The
stray packages/db/parking.sqlite was untracked + already gitignored (*.sqlite);
deleted it from disk. Now `pnpm --filter @parking/db db:migrate` targets the
appliance DB out of the box.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

packages/db/package.json

@@ -21,7 +21,7 @@
     "typecheck": "tsc --noEmit",
     "lint": "tsc --noEmit",
     "db:generate": "drizzle-kit generate",
-    "db:migrate": "drizzle-kit migrate"
+    "db:migrate": "DATABASE_URL=\"${DATABASE_URL:-../../apps/server/parking.sqlite}\" drizzle-kit migrate"
   },
   "dependencies": {
     "@parking/shared": "workspace:*",