Add incoming webhooks, fix stale service worker and push re-registration

- Webhooks for automations: per-job secret, Gitea/GitHub HMAC signatures,
  payload appended to the instructions; settings on the automations page
- Service worker gets a new file name per build (proxies that cache *.js
  served a stale worker, which broke updates and Android installation);
  /sw.js is a kill switch that removes old workers
- Push: devices re-register their subscription with the server on start and
  before a test; the test reports why a push service rejected a message

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/i18n/en.ts

@@ -410,6 +410,13 @@ export const en = {
   "install.hint.firefox": "Firefox can't install web apps – open CodeCraft in Chrome (Android) or use “Add to home screen”.",
   "install.hint.ios": "Safari: Share button → “Add to Home Screen”. Push notifications work only in the installed app.",
   "install.hint.desktop": "Chrome/Edge: install icon in the address bar or menu → “Install CodeCraft”.",
+  "settings.pushTestFailed": "The push service rejected the notification",
+  "jobs.webhook": "Webhook",
+  "jobs.webhookOn": "Enable webhook",
+  "jobs.webhookOff": "Disable webhook",
+  "jobs.webhookRenew": "New secret",
+  "jobs.webhookShown": "Copy the secret now – it is shown only once:",
+  "jobs.webhookHelp": "POST any JSON to the URL; it is appended to the instructions. Authenticate with the header X-CodeCraft-Secret (or ?secret=…), or enter the secret as webhook secret in Gitea/GitHub (signature X-Gitea-Signature / X-Hub-Signature-256).",
   "new.title": "New session",
   "new.directory": "Project directory",
   "new.up": "Up",