Replace Clay with n8n, Ollama, SearXNG and browserless; add Telegram assistant

Remove the Clay role (Claude Code web UI) and its Anthropic API key.

New roles:
- ollama: local CPU LLM (qwen3:4b-instruct), internal network only
- browserless: headless Chromium for JavaScript-heavy pages
- searxng: metasearch backend for the chat web_search tool
- n8n at agent.ladkau.de: web chat (/chat), scheduled workflows,
  Telegram bot; workflows and credentials are imported from the repo

Telegram bot: Gemini 3.8 -> Gemini 3.5 -> local Qwen fallback chain,
/qwen to force the local model, /stocks and a weekday schedule
(07:30, 13:00, 17:40) for the MTE.DE / PTX.F stock report.

Also: dashboard and check-services entries for the chat, vault checks
for the new secrets (n8n, SearXNG, Gemini, Telegram, SMTP), updated
CLAUDE.md, runbooks and README.

scripts/check-vault.sh

@@ -44,7 +44,13 @@ required_scalars = [
     "roundcube_db_password",
     "roundcube_des_key",
     "vaultwarden_admin_token",
-    "anthropic_api_key",
+    "n8n_encryption_key",
+    "searxng_secret_key",
+    "smtp_user",
+    "smtp_password",
+    "gemini_api_key",
+    "telegram_bot_token",
+    "telegram_user_id",
 ]
 
 # Required non-empty lists (must contain at least one entry)
@@ -52,7 +58,7 @@ required_lists = [
     "traefik_dashboard_users",
     "registry_users",
     "dovecot_users",
-    "clay_users",
+    "n8n_users",
 ]
 
 # Optional scalars: validated only when present — (key, validator_fn, hint)