3.x.x: CI doesn't run generate_prism_alerts.py --check, and the load harness side report omits the median tip gate (#805) #817

These are two low-severity CI and tooling gaps found in the review of #811 (head 4ddeb762). Line numbers are at 4ddeb762.

1. CI doesn't run generate_prism_alerts.py --check.

   • What depends on it: 3.x.x: gate the revision-work warnings on recent miners and end a lost settlement race's unknown wait (#758) #800 relies on the check to keep these in sync:
     • the revision-work expressions;
     • the 15-minute window prose;
     • the migration tables;
     • the qbit-tools patch's specification digest.
   • What CI runs instead: ci.yml L49-L67 runs only test_prism_alert_promql.py and check_prism_alert_uids.py, and no test calls the generator.
   • What CI misses: each of these keeps CI green:
     • a hand edit to docs/prism-native-alert-rules.json;
     • a change to MINER_WINDOW_MINUTES without the docs;
     • a patch that wasn't regenerated.
   • At 4ddeb762, --check exits 0.
   • Fix: run python3 scripts/generate_prism_alerts.py --check beside the UID check in lint-compile-compose.

2. The load harness's side report leaves out the new median gate (3.x.x: gate the real-node smoke on a median it can support and print where a slow tip's time went (#790) #805).

   • run.rs L2706-L2713 writes preset.gates without tip_last_notify_median_budget_ms. Two churn and new-session keys were already missing.
   • So a real-node-smoke load-harness-report.json shows only tip_last_notify_p99_budget_ms: 10000, which reads as a 10 s gate.
   • The verdicts themselves are correct, because they rebuild the budgets from the preset.
   • Fix: write the whole gates block (derive Serialize), or add the missing keys.