Expose optional project_id on generation requests

app/generation/schemas/requests.py

@@ -31,6 +31,10 @@ class GenerationRequestCreate(BaseModel):
         default=None,
         pattern=(r"^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-" r"[89ab][0-9a-f]{3}-[0-9a-f]{12}$"),
     )
+    project_id: str | None = Field(
+        default=None,
+        pattern=(r"^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-" r"[89ab][0-9a-f]{3}-[0-9a-f]{12}$"),
+    )
     brand_kit_version_id: str | None = Field(default=None, min_length=1, max_length=36)
     # Concrete-provider controls remain closed, typed schemas rather than an
     # escape hatch for arbitrary worker payload. Provider-specific fields must