refactor(db): switch records layer to Prisma

- Replace hand-written node:sqlite queries with a Prisma client using
  the better-sqlite3 driver adapter
- Version the schema with migrations: baseline table, timestamp
  normalisation, and WAL journal mode
- Store timestamps with an explicit UTC offset so they stop being parsed
  as local time
- Show created/updated times on the edit page, formatted with dayjs
- Move the root redirect into next.config to avoid a prerender error
- Run migrations from the container entrypoint before starting the server

BREAKING CHANGE: DNSMASQ_ADMIN_DB_PATH is replaced by DATABASE_URL, which
must be a Prisma connection URL (file:./data/dnsmasq-admin.db). Existing
database files are migrated in place and need no conversion.

.env.example

@@ -1,8 +1,16 @@
-# Copy to .env.local and adjust for your setup. Every value is optional — the app falls back
-# to local paths under ./data so it runs with no configuration at all.
+# Copy to .env (NOT .env.local) and adjust for your setup.
+#
+# Why .env and not .env.local: Next.js reads both, but the Prisma CLI only reads whatever its
+# config file loads — prisma.config.ts imports dotenv/config, which reads `.env`. Keeping
+# DATABASE_URL there means `prisma migrate deploy` and the app agree on the same database.
+#
+# Every value below is optional except DATABASE_URL — the app falls back to local paths under
+# ./data so it runs with almost no configuration.
 
-# SQLite database — the single source of truth for records. Docker: /data/dnsmasq-admin.db
-DNSMASQ_ADMIN_DB_PATH=./data/dnsmasq-admin.db
+# Prisma connection URL for the SQLite database — the single source of truth for records.
+# Docker: /data/dnsmasq-admin.db
+# Relative paths resolve against the project root, not prisma/schema.prisma.
+DATABASE_URL="file:./data/dnsmasq-admin.db"
 
 # Managed dnsmasq config file this app regenerates on every apply.
 # Docker: /etc/dnsmasq.d/dnsmasq-admin.conf