fix: address CodeRabbit review for per-site probe

- Fix SSE abort: propagate AbortSignal to worker pool; close connection
  immediately on client disconnect without sending 'complete' event
- Fix Boolean coercion: use strict === true/=== 1 check instead of Boolean()
  to avoid Boolean('false') === true foot-gun
- Fix probe-now: parse and forward latencyThresholdMs from request body
- Fix api.ts probeSiteNow: add latencyThresholdMs to options type
- Fix backup import: restore postRefreshProbe* fields when inserting sites
  so that backup/restore round-trips preserve per-site probe config
- Fix latency threshold persistence: add postRefreshProbeLatencyThresholdMs
  column (migration 0026), save/load it in site editor, pass to
  runPostRefreshProbeIfEnabled so auto-probe also respects the threshold
- Fix state management: setProbeCompleted(false) at probe start; error
  branch also refreshes model lists and sets probeCompleted to show results
- Regenerate schema artifacts (mysql/postgres bootstrap+upgrade, contract)

drizzle/meta/_journal.json

@@ -176,6 +176,13 @@
       "when": 1776943800000,
       "tag": "0025_site_post_refresh_probe",
       "breakpoints": true
+    },
+    {
+      "idx": 25,
+      "version": "6",
+      "when": 1776944000000,
+      "tag": "0026_site_probe_latency_threshold",
+      "breakpoints": true
     }
   ]
 }