feat(quotas): admin quota API and GET /api/user/quota

Admins read and set the instance default, team allowances and user
overrides under /api/admin/quotas. A user's endpoint also returns the
limits those layers resolve to, the layer each came from and the usage
against them. The overview lists catalog models used this period that have
no price, since a cost limit cannot see them. Every write is audited.

GET /api/user/quota gives a user their own limited buckets, usage and reset
time without naming the policies behind them; any valid token may call it.

docsgpt/api/admin/__init__.py

@@ -1,3 +1,4 @@
 from .routes import admin_ns
+from . import quotas  # noqa: F401  (registers the quota resources on admin_ns)
 
 __all__ = ["admin_ns"]