fix: unset placeholder DATABASE_URL after prisma:generate so build/migrate use real .env

prisma:generate needs DATABASE_URL to resolve the schema but doesn't
connect to the DB. After generate, unset the placeholder so that
pnpm build and pnpm db:migrate pick up the real DATABASE_URL from
the live .env (symlinked into the stage directory).

.gitea/workflows/deploy.yaml

@@ -336,9 +336,12 @@ jobs:
           echo "STAGE DATABASE_POOL_SIZE=${DATABASE_POOL_SIZE}"
 
            pnpm install --frozen-lockfile
-           # Stage symlinks to live .env, so DATABASE_URL is already the real value.
-           # prisma generate only needs the URL for client generation — no live DB connection.
+           # prisma generate only needs DATABASE_URL to resolve the schema — no live DB connection.
+           # Use a placeholder so it doesn't fail if .env isn't loaded yet; db:migrate later
+           # will use the real DATABASE_URL from the live .env symlink.
+           export DATABASE_URL="mysql://placeholder:please@localhost/placeholder"
            pnpm prisma:generate
+           unset DATABASE_URL
           export BCRYPT_ROUNDS=4
           pnpm typecheck
           # Validate production env (AUTH_SECRET, DATABASE_URL, …) during build.