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>

package.json

@@ -25,9 +25,6 @@
     "format": "prettier --write .",
     "format:check": "prettier --check ."
   },
-  "prisma": {
-    "seed": "tsx prisma/seed.ts"
-  },
   "keywords": [],
   "author": "",
   "license": "ISC",
@@ -47,7 +44,8 @@
     "@fastify/static": "^9.0.0",
     "@mui/material": "^7.3.11",
     "@mui/x-date-pickers": "^8.29.0",
-    "@prisma/client": "^6.19.2",
+    "@prisma/adapter-mariadb": "^7.8.0",
+    "@prisma/client": "^7.8.0",
     "@tanstack/react-query": "^5.100.5",
     "@types/jsdom": "^28.0.1",
     "bcryptjs": "^3.0.3",
@@ -60,10 +58,11 @@
     "jsdom": "^29.0.2",
     "jsonwebtoken": "^9.0.3",
     "leaflet": "^1.9.4",
+    "mariadb": "^3.5.2",
     "node-cron": "^4.2.1",
     "nodemailer": "^8.0.2",
     "otpauth": "^9.5.0",
-    "prisma": "^6.19.2",
+    "prisma": "^7.8.0",
     "puppeteer": "^24.40.0",
     "qrcode": "^1.5.4",
     "react": "^19.2.7",