ai-stack: vendor the local-ai full AI stack as a new service

Vendor the functional source of github.com/outis1one/local-ai into
./ai-stack (22 files) and add services/ai-stack.sh, which copies the
source to ~/docker/ai-stack and hands off to the app's VRAM-aware
installer (local-ai-setup.sh). The stack bundles Ollama, Open WebUI,
RAG + MCP servers, ChromaDB, SearXNG, Kiwix, Gitea, InvokeAI, ComfyUI
and Portainer.

Cloud LLM providers (Groq/DeepInfra/OpenAI/OpenRouter) are optionally
wired into Open WebUI via the plural OPENAI_API_BASE_URLS list, with the
local RAG connection kept as the first entry so RAG keeps working. Open
WebUI ships built-in auth, so Caddy is configured without Authelia.

Excludes the upstream's two bundled copies of this very project
(ubuntu-post-install.sh, ubuntu-post-install-main.zip) — stale and
circular. Coexists with the existing ai-gpu service.

Also fix the install-function names for ai-gpu and ai-stack: the
dispatcher calls install_<raw-name>, so the function must be
install_ai-gpu / install_ai-stack (hyphen), matching the working
mail-archiver / wg-easy services. ai-gpu was previously uninstallable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nb2vJ8W7bHKx1JXVvpCraH

ai-stack/systemd/kiwix-update.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Monthly Kiwix ZIM update check
+Requires=kiwix-update.service
+
+[Timer]
+OnCalendar=monthly
+RandomizedDelaySec=1h
+Persistent=true
+
+[Install]
+WantedBy=timers.target