feat(chat): replace built-in chat with LibreChat SSO integration

Replaces the custom chat page with an external LibreChat instance that
shares Keycloak SSO for seamless auto-login. Removes Tools and Knowledge
Base pages as these are now handled by LibreChat's built-in capabilities.

- Add LibreChat service to docker-compose with Ollama backend config
- Add Keycloak OIDC client (certifai-librechat) with prompt=none for
  silent SSO
- Create librechat.yaml with CERTifAI branding, Ollama endpoint, and
  custom page title/logo
- Change sidebar Chat link to external URL (opens LibreChat in new tab)
- Remove chat page, tools page, knowledge base page and all related
  components (chat_sidebar, chat_bubble, chat_input_bar, etc.)
- Remove tool_card, file_row components and tool/knowledge models
- Remove chat_stream SSE handler (no longer needed)
- Clean up i18n files: remove chat, tools, knowledge sections
- Dashboard article summarization via Ollama remains intact

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -39,6 +39,11 @@ SEARXNG_URL=http://localhost:8888
 OLLAMA_URL=http://localhost:11434
 OLLAMA_MODEL=llama3.1:8b
 
+# ---------------------------------------------------------------------------
+# LibreChat (external chat via SSO) [OPTIONAL - default: http://localhost:3080]
+# ---------------------------------------------------------------------------
+LIBRECHAT_URL=http://localhost:3080
+
 # ---------------------------------------------------------------------------
 # LLM Providers (comma-separated list) [OPTIONAL]
 # ---------------------------------------------------------------------------