Drop self-hosted AI (Ollama + SearXNG); gregtime switches to xAI Grok

The Ollama role and SearXNG container backed FISTO AI responses in the
greg-time Discord bot. greg-time 3.9.6 drops both (plus the Gemini path)
in favor of a single xAI Grok backend, so:

- remove the ollama role and its wiring in deploy_home.yml
- remove the searxng container task, template, and searxng_path default
- gregtime: swap OLLAMA_*/SEARXNG_URL/GEMINI_API_KEY env for XAI_API_KEY,
  bump image 3.6.5 -> 3.9.6
- vault: add xai_api_key, drop gemini_api_key

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ansible/roles/podman/tasks/containers/home/gregtime.yml

@@ -40,14 +40,8 @@
       - host
     env:
       TZ: America/New_York
-      # Ollama + SearXNG for FISTO AI responses
-      OLLAMA_HOST: "http://127.0.0.1:11434"
-      OLLAMA_MODEL: "dolphin-mistral"
-      OLLAMA_FALLBACK_MODEL: "dolphin-phi"
-      OLLAMA_NUM_PREDICT: "300"
-      SEARXNG_URL: "http://127.0.0.1:8080"
-      # Gemini API for @bot gemini command
-      GEMINI_API_KEY: "{{ gemini_api_key }}"
+      # xAI Grok API — the bot's sole AI backend
+      XAI_API_KEY: "{{ xai_api_key }}"
       # Zomboid RCON configuration for Discord restart command
       ZOMBOID_RCON_HOST: "127.0.0.1"
       ZOMBOID_RCON_PORT: "{{ zomboid_rcon_port }}"