chore(deps): upgrade Prisma 6.19 -> 7.8.0 (Rust-free client + mariadb adapter)

prisma / @prisma/client 6.19.2 -> 7.8.0; added @prisma/adapter-mariadb 7.8.0 and
mariadb 3.5.2 (the runtime driver).

Prisma 7 breaking changes handled (verified via Prisma's own tooling — the
official upgrade-guide summary had hallucinated package names, so I confirmed
everything against `prisma validate`/`generate` and the installed type defs):

- The Rust query engine is removed; the runtime connection is now made through a
  driver adapter. src/config/database.ts wires PrismaMariaDb, parsing
  DATABASE_URL into an explicit mariadb pool config so the literal `@` in our
  password (which a naive connection-string parser mishandles) is correct.
- datasource `url` is no longer allowed in schema.prisma -> moved to a new
  prisma.config.ts (schema + datasource.url + migrations.seed). Prisma 7 no
  longer auto-loads .env, so the config does `import "dotenv/config"`.
- The deprecated package.json#prisma seed config was removed (now in the config).
- seed.ts and the two maintenance scripts now use the shared adapter-wired client.

The legacy `prisma-client-js` generator STILL works under v7 (generates to
@prisma/client as before), so NO import-path changes were needed across the 16
@prisma/client import sites — switching to the new prisma-client/output generator
is not required for us. No prisma.$use() middleware exists. Node 24 / TS 5.9
exceed the v7 minimums (20.19 / 5.4).

No migrations were run (your DBs are untouched); removing datasource.url is a
config change, not DDL, so this phase needs no new migration.

Gates: tsc 0 | build 0 | vitest 247/247 against app_test (proves the mariadb
adapter works at runtime, incl. raw SELECT...FOR UPDATE locking and Decimal/VAT)
| eslint 0 errors.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/config/database.ts

@@ -1,6 +1,27 @@
 import { PrismaClient } from "@prisma/client";
+import { PrismaMariaDb } from "@prisma/adapter-mariadb";
+
+// Prisma 7 removed the Rust query engine; the runtime DB connection is now made
+// through a driver adapter. PrismaMariaDb wraps the `mariadb` driver (which is
+// MySQL-wire compatible). We parse DATABASE_URL ourselves and pass an explicit
+// pool config rather than the raw connection string, so a literal `@` in the
+// password (which a naive connection-string parser would mishandle) is handled
+// correctly.
+function mariadbAdapterFromUrl(rawUrl: string): PrismaMariaDb {
+  const u = new URL(rawUrl);
+  return new PrismaMariaDb({
+    host: u.hostname,
+    port: u.port ? Number(u.port) : 3306,
+    user: decodeURIComponent(u.username),
+    password: decodeURIComponent(u.password),
+    database: u.pathname.replace(/^\//, ""),
+  });
+}
+
+const adapter = mariadbAdapterFromUrl(process.env.DATABASE_URL as string);
 
 const prisma = new PrismaClient({
+  adapter,
   log: process.env.APP_ENV === "local" ? ["warn", "error"] : ["error"],
 });