Scan runs

Read scan history, status, and model coverage.

`GET /v1/brands/{brand_id}/scan-runs`

One item per user-facing scan (scan_cycle_metrics), newest first.

Query	Values
`status`	`queued`, `running`, `succeeded`, `partial`, `failed`, `cancelled`
`from`, `to`	RFC 3339; applied to `completed_at`, or `created_at` for unfinished scans
`limit`, `cursor`	keyset

Returns scan_run. No model transcripts or raw responses are ever returned. Failures are reduced to { "code": "scan_failed" }.

Adds model_runs[] (up to 50 per-model runs, with progress and metrics).