Add dns_txt, webrtc_mesh, and wsus_cache_peer LOTL deploy tiers with Forge toggles.

Implements three new spread lanes following the do_peer pattern: DNS TXT mesh staging, WebRTC LAN seed manifest delivery, and WSUS SoftwareDistribution cousin handoff. Integrates tiers into onion chain, deploy-plan allowlist, Forge UI/docs, and tests.

server/web/src/help/uiHelp.test.ts

@@ -93,6 +93,7 @@ describe('UI_HELP', () => {
     'set_alerts',
     'set_alert_notifications',
     'set_webhook',
+    'crucible_section_spread_templates',
   ] as const;
 
   it('defines help for every documented UI key', () => {