Show: every clip around this alarm across chosen cameras, stably paged

The Show scene for one alarm (event_id is the anchor): every clip at the anchor's site in a window, open queue alarms and closed context (reviewed, filtered, agent_closed, classified exactly like GET /events/{id}/around) merged in ONE oldest-first pass on (created_at, id), so an alarm that closes between pages is returned once. until=anchor (default): window = anchor time minus before_seconds to plus after_seconds; until=now: the last before_seconds up to the snapshot (after_seconds ignored). camera_id (repeatable, at most 50, at the anchor's site) narrows the scene; the anchor's camera is always included; absent = every camera at the site. Membership, paging and the error rules mirror GET /events/open-alarms: every page bounds clips by creation time (created_at <= snapshot.as_of) and by current membership at that page's read (open, or closed context); a clip created at or before as_of that only becomes visible or closed after it is returned if its key is still ahead of the cursor; counts (total, by_state, by_camera) are page-one observations (total and by_state repeat unchanged from page one on later pages; by_camera is returned on page one only) and the rows returned can differ from them; on truncated, omitted is the eligible clips after the last returned one at that read (a lower bound when omitted_capped). A 200 is always a true statement, anything else is UNKNOWN, never an empty scene. Items carry media REFERENCES only (media.clip_url_path, media.snapshot_path): no presign, no S3 call, no video. Central staff only; the anchor goes through the same scope check as /around (out of scope, demo and unknown are one 404) and every row is tenant-scoped in SQL on every page. Read-only: Show never acquires, claims or marks viewed what it displays. Capability: alarm_show_read on GET /auth/me.