Change the traffic chart API response from bucket-based to series-based
to better support frontend visualization libraries. The new format
provides a shared X-axis and aligned data arrays for each model series.
- Replace `buckets` with `x` and `series` in response
- Implement data alignment and zero-filling for time slots
- Update Swagger documentation including pending definitions
BREAKING CHANGE: The `GET /admin/logs/stats/traffic-chart` response
schema has changed. `buckets` and `models` fields are removed.
Organize admin panel feature documentation into a dedicated directory
and include an interactive HTML mockup along with a reference
screenshot for the EZ-API Control Plane Dashboard.
