refactor(triggers): review followups — fire-now, dedupe trigger pages, hardening

Follow-ups on commit 39e1e36 addressing review feedback from
go-reviewer / security-reviewer / typescript-reviewer.

Backend:
- New POST /api/triggers/{id}/fire (AdminOnly, schedule-only): operator
  "Fire now" button — dispatches immediately without waiting for the
  next natural interval. Persists last_fired_at BEFORE dispatch, same
  ordering as the scheduler. Per-trigger in-flight guard (429 if a
  fire is already running) to defend against rapid double-clicks /
  runaway scripts. Refuses request when AdminOnly claims are absent
  rather than logging an unattributable deploy.
- SetTriggerLastFired now validates timestamp parses as RFC3339 before
  writing. Rejects empty string explicitly — empty-clears semantics
  were dead (no caller) and would silently re-fire on next tick if
  ever accidentally written. A future reset-cadence flow must add a
  dedicated ClearTriggerLastFired so the call site is grep-able and
  separately auditable.
- Scheduler logs WARN on catch-up fires (now - lastFired > 2× interval)
  so the "surprise burst at restart" pattern shows up in audit logs.
- BindingResult reason strings extracted to package consts
  (webhook.Reason*) so the scheduler and api fire-now classifications
  stay in sync without string-matching drift.
- SECURITY NOTE on FanOutForTrigger documents that the
  WebhookRequireSignature gate is ingress-only by design.

Frontend:
- Refactored /triggers/new (770 LOC → 155 LOC) and /triggers/[id]
  (~350 LOC dropped) to use the shared TriggerKindForm. Eliminates the
  triplicated per-kind state + buildConfig + canSubmit + template that
  caused the d-unit regex drift in the prior commit.
- New seedTriggerKindFormState helper on TriggerKindForm primes the
  form from a server-returned trigger config with defensive type
  guards; resets per-kind slots first so re-seeding across kinds
  doesn't inherit stale state.
- /triggers/[id] gains a Schedule status panel with Last Fired + Fire
  Now button (gated on binding_count > 0). Confirmation dialog,
  result flash, timer cleanup on unmount + new-fire (no stale-closure
  race). EN+RU i18n parity.

cmd/server/main.go

@@ -197,7 +197,7 @@ func main() {
 			switch {
 			case r.Deployed:
 				deployed++
-			case r.Reason == "binding disabled", r.Reason == "no match":
+			case r.Reason == webhook.ReasonBindingDisabled, r.Reason == webhook.ReasonNoMatch:
 				// not a failure — silent
 			default:
 				errored++