Subscribe to the admin aggregate live event stream (SSE)

Consumes a ticket from POST /api/v1/admin/events/ticket and upgrades the response to an SSE stream that delivers every event published for every account. Used by the back-office dot-grid dashboard at app.uptimemonitoring.com/ops (SPEC §Back-Office Dashboard).

Each frame carries the same envelope as /api/v1/events/stream (see docs/SSE_LIVE_UPDATES_SPEC.md §6 + §7); account_id identifies the originating account. Heartbeat comments (: heartbeat) are emitted every 25 s.

Admin membership is re-checked at stream-open time against the durable admins table — a row deleted in the 0-30s ticket-redeem window cannot keep a long-lived connection alive. Also re-checked periodically while connected (issue #339): once open, the same account/membership/key check plus the admin-lookup check both re-run every ~30 seconds. Removing the minting admin's account membership, revoking their API key, suspending the account, or deleting their admins row closes an already-open admin stream within roughly 45 seconds on a healthy connection (detected within ~35 seconds by the recheck, plus up to a further 10s write deadline for an in-flight write/flush to unblock and the stream to actually close) — not instantly, not a hard worst case (the write deadline is armed only for the duration of a write+flush and cleared between frames, so a stalled HTTP/2 connection writer is not bounded by it), and never due to a merely transient error (e.g. a database hiccup), which only delays how soon a genuine revocation takes effect.