feat(backup): take Tinyforge DB snapshot before every deploy

Adds an opt-in "auto_backup_before_deploy" setting that triggers a
"pre-deploy" backup at the start of every project deploy via the deploy
pipeline (covers both the async HTTP path and the sync poller/webhook
path). Failures are logged to the deploy log but do not abort — missing
a backup is preferable to refusing to ship a fix.

- store: settings.auto_backup_before_deploy column + scan/update wiring
- backup: accept "pre-deploy" as a valid backup_type
- deployer: small PreDeployBackuper interface, hooked into runDeploy
  right after settings load and before any state-mutating work
- api: settings request/response surface the new flag
- web: ToggleSwitch on the backup settings page; "Pre-deploy" badge
  variant in the backup list (badge-warning so it stands out)
- i18n: en/ru strings for the toggle, help text, and badge label

internal/store/store.go

@@ -147,6 +147,10 @@ func (s *Store) runMigrations() error {
 		`ALTER TABLE stages ADD COLUMN notification_secret TEXT NOT NULL DEFAULT ''`,
 		`ALTER TABLE static_sites ADD COLUMN notification_url TEXT NOT NULL DEFAULT ''`,
 		`ALTER TABLE static_sites ADD COLUMN notification_secret TEXT NOT NULL DEFAULT ''`,
+		// Auto-backup before deploy (2026-05-07). When enabled, the deployer
+		// triggers a "pre-deploy" Tinyforge DB backup before any project deploy
+		// so a corrupted deploy is recoverable without data loss.
+		`ALTER TABLE settings ADD COLUMN auto_backup_before_deploy INTEGER NOT NULL DEFAULT 0`,
 	}
 
 	// Additive stack tables (2026-04-16). Created here rather than in the