Add BCRYPT_ROUNDS env override, use 4 in CI

- Bcrypt rounds now configurable via BCRYPT_ROUNDS env var (default 12)
- CI/deploy use BCRYPT_ROUNDS=4 for faster tests
- Argon2 test: 1161ms → 17ms (already done)
- Password test suite: 1860ms → 1330ms

.gitea/workflows/ci.yaml

@@ -32,6 +32,7 @@ jobs:
           export SKIP_ENV_VALIDATION=1
           export ARGON2_MEMORY_SIZE=1024
           export ARGON2_ITERATIONS=1
+          export BCRYPT_ROUNDS=4
           pnpm install --frozen-lockfile
           pnpm prisma:generate
           pnpm biome:lint