When a generated entity schema declares a default value for a field, the
mock generator now returns it verbatim instead of a faker-generated random.
This restores parity with `@almadar/runtime`'s MockPersistenceAdapter so
fields like `tokenCount : number = 0` show 0 in compiled-path screenshots
instead of a random number that contradicts what runtime-verify sees.

The special string sentinel `"@now"` resolves to the current ISO timestamp,
matching the existing convention in the runtime path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>