feat(chat): add LLM-powered travel agent with multi-provider support

Implement a full chat-based travel agent using LiteLLM for multi-provider
LLM support (OpenAI, Anthropic, Gemini, Ollama, Groq, Mistral, etc.).

Backend:
- New 'chat' Django app with ChatConversation and ChatMessage models
- Streaming SSE endpoint via StreamingHttpResponse
- 5 agent tools: search_places, list_trips, get_trip_details,
  add_to_itinerary, get_weather
- LiteLLM client wrapper with per-user API key retrieval
- System prompt with user preference context injection

Frontend:
- New /chat route with full-page chat UI (DaisyUI + Tailwind)
- Collapsible conversation sidebar with CRUD
- SSE streaming response display with tool call visualization
- Provider selector dropdown
- SSE proxy fix to stream text/event-stream without buffering
- Navbar link and i18n keys

frontend/src/routes/api/[...path]/+server.ts

@@ -86,11 +86,20 @@ async function handleRequest(
 			});
 		}
 
-		const responseData = await response.arrayBuffer();
-		// Create a new Headers object without the 'set-cookie' header
+		const contentType = response.headers.get('content-type') || '';
 		const cleanHeaders = new Headers(response.headers);
 		cleanHeaders.delete('set-cookie');
 
+		// Stream SSE responses through without buffering
+		if (contentType.includes('text/event-stream')) {
+			return new Response(response.body, {
+				status: response.status,
+				headers: cleanHeaders
+			});
+		}
+
+		const responseData = await response.arrayBuffer();
+
 		return new Response(responseData, {
 			status: response.status,
 			headers: cleanHeaders