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.

prisma/migrations/0001_baseline/migration.sql

@@ -0,0 +1,31 @@
+-- Baseline: the `records` table as Prisma itself generates it from prisma/schema.prisma.
+--
+-- This SQL is kept byte-identical to the output of
+--   `prisma migrate diff --from-empty --to-schema prisma/schema.prisma --script`
+-- on purpose. The alternative — adding `COLLATE NOCASE` on `domain` and a
+-- `CHECK (type IN ('A','CNAME'))` by hand — makes Prisma see permanent drift and propose a
+-- DROP TABLE + rebuild migration the next time anyone runs `migrate dev`, which would silently
+-- drop those very constraints. A clean diff is worth more here than the extra constraints,
+-- because both properties are enforced elsewhere:
+--
+--   - case-insensitive uniqueness: lib/validate.ts lowercases every domain before it reaches
+--     the database, so `FOO.com` and `foo.com` can never both be inserted;
+--   - case-insensitive ordering: lib/records.ts sorts with localeCompare after fetching,
+--     since SQLite would otherwise order by binary collation ('Zoo' before 'apple');
+--   - the type whitelist: again lib/validate.ts, plus the generated union in lib/db.ts.
+--
+-- Existing databases installed before this migration already ran the earlier hand-written
+-- version and keep their column-level COLLATE NOCASE; nothing about them changes.
+CREATE TABLE "records" (
+    "id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
+    "domain" TEXT NOT NULL,
+    "type" TEXT NOT NULL,
+    "value" TEXT NOT NULL,
+    "enabled" BOOLEAN NOT NULL DEFAULT true,
+    "comment" TEXT NOT NULL DEFAULT '',
+    "created_at" DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updated_at" DATETIME NOT NULL
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "records_domain_key" ON "records"("domain");