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

backend/server/chat/migrations/0001_initial.py

@@ -0,0 +1,90 @@
+# Generated by Django 5.2.12 on 2026-03-08
+
+import django.db.models.deletion
+import uuid
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    initial = True
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="ChatConversation",
+            fields=[
+                (
+                    "id",
+                    models.UUIDField(
+                        default=uuid.uuid4,
+                        editable=False,
+                        primary_key=True,
+                        serialize=False,
+                    ),
+                ),
+                ("title", models.CharField(blank=True, default="", max_length=255)),
+                ("created_at", models.DateTimeField(auto_now_add=True)),
+                ("updated_at", models.DateTimeField(auto_now=True)),
+                (
+                    "user",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="chat_conversations",
+                        to=settings.AUTH_USER_MODEL,
+                    ),
+                ),
+            ],
+            options={
+                "ordering": ["-updated_at"],
+            },
+        ),
+        migrations.CreateModel(
+            name="ChatMessage",
+            fields=[
+                (
+                    "id",
+                    models.UUIDField(
+                        default=uuid.uuid4,
+                        editable=False,
+                        primary_key=True,
+                        serialize=False,
+                    ),
+                ),
+                (
+                    "role",
+                    models.CharField(
+                        choices=[
+                            ("user", "User"),
+                            ("assistant", "Assistant"),
+                            ("system", "System"),
+                            ("tool", "Tool"),
+                        ],
+                        max_length=20,
+                    ),
+                ),
+                ("content", models.TextField(blank=True, default="")),
+                ("tool_calls", models.JSONField(blank=True, null=True)),
+                (
+                    "tool_call_id",
+                    models.CharField(blank=True, max_length=255, null=True),
+                ),
+                ("name", models.CharField(blank=True, max_length=255, null=True)),
+                ("created_at", models.DateTimeField(auto_now_add=True)),
+                (
+                    "conversation",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="messages",
+                        to="chat.chatconversation",
+                    ),
+                ),
+            ],
+            options={
+                "ordering": ["created_at"],
+            },
+        ),
+    ]