refactor: replace Prisma ORM runtime with Drizzle ORM facade

- Replace Prisma client runtime with Drizzle ORM (zero Prisma engine/query engine in production)
- Add Prisma-compatible facade (@/lib/prisma-facade.ts) backed by Drizzle for backwards compatibility
- Runtime queries route through Drizzle ORM; @prisma/client is now devDependency (types only)
- Remove @prisma/adapter-mariadb dependency; delete prisma-pool.ts and types/prisma.ts
- New Drizzle schema layer: src/db/schema.ts (176 tables) and src/lib/db.ts (connection)
- Update README documenting the dual-layer ORM architecture
- Restore src/generated/ gitignore (build artifact for local type generation)
- 0 TypeScript errors, 583 tests passing

The facade intentionally uses `any` types to match the Prisma Client API surface,
allowing existing code to run unmodified while routing queries through Drizzle at runtime.

src/lib/db-pool.ts

@@ -0,0 +1,16 @@
+/**
+ * Cap pool size during `next build` so N workers × pool don't exhaust MySQL.
+ * Kept free of driver/env imports so unit tests can exercise it in isolation.
+ */
+export function resolveConnectionLimit(
+	poolSize: number,
+	phase = process.env.NEXT_PHASE,
+): number {
+	if (
+		phase === "phase-production-build" ||
+		phase === "phase-production-compile"
+	) {
+		return Math.min(poolSize, 5);
+	}
+	return poolSize;
+}