fix(ai): critical fixes for agent-redesign - provider selection and auto-learn

Fix 1: Provider/Model Selection (Critical - unblocks LLM)
- Add /api/chat/providers/{id}/models/ endpoint to fetch available models
- Auto-select first configured provider instead of hardcoded 'openai'
- Add model dropdown populated from provider API
- Filter provider list to only show configured providers
- Show helpful error when no providers configured

Fix 2: Auto-Learn Preferences (Replaces manual input)
- Create auto_profile.py utility to infer preferences from user data
- Learn interests from Activity sport types and Location categories
- Learn trip style from Lodging types (hostel=budget, resort=luxury, etc.)
- Learn geographic preferences from VisitedRegion/VisitedCity
- Call auto-learn on every chat start (send_message)
- System prompt now indicates preferences are auto-inferred

Fix 3: Remove Manual Preference UI
- Remove travel_preferences section from Settings
- Remove preference form fields and save logic
- Remove preference fetch from server-side load
- Keep UserRecommendationPreferenceProfile type for backend use

The LLM should now work correctly:
- Users with any configured provider will have it auto-selected
- Model list is fetched dynamically from provider API
- Preferences are learned from actual travel history

backend/server/integrations/utils/__init__.py

@@ -0,0 +1,7 @@
+from rest_framework.pagination import PageNumberPagination
+
+
+class StandardResultsSetPagination(PageNumberPagination):
+    page_size = 25
+    page_size_query_param = "page_size"
+    max_page_size = 1000

backend/server/integrations/utils/auto_profile.py

@@ -0,0 +1,168 @@
+"""
+Auto-learn user preferences from their travel history.
+"""
+
+import logging
+
+from django.db.models import Count
+
+from adventures.models import Activity, Location, Lodging
+from integrations.models import UserRecommendationPreferenceProfile
+from worldtravel.models import VisitedCity, VisitedRegion
+
+logger = logging.getLogger(__name__)
+
+
+# Mapping of lodging types to travel styles
+LODGING_STYLE_MAP = {
+    "hostel": "budget",
+    "campground": "outdoor",
+    "cabin": "outdoor",
+    "camping": "outdoor",
+    "resort": "luxury",
+    "villa": "luxury",
+    "hotel": "comfort",
+    "apartment": "independent",
+    "bnb": "local",
+    "boat": "adventure",
+}
+
+# Activity sport types to interest categories
+ACTIVITY_INTEREST_MAP = {
+    "hiking": "hiking & nature",
+    "walking": "walking tours",
+    "running": "fitness",
+    "cycling": "cycling",
+    "swimming": "water sports",
+    "surfing": "water sports",
+    "kayaking": "water sports",
+    "skiing": "winter sports",
+    "snowboarding": "winter sports",
+    "climbing": "adventure sports",
+}
+
+
+def build_auto_preference_profile(user) -> dict:
+    """
+    Automatically build preference profile from user's existing data.
+
+    Analyzes:
+    - Activities (sport types) → interests
+    - Location categories → interests
+    - Lodging types → trip style
+    - Visited regions/cities → geographic preferences
+
+    Returns dict with: cuisines, interests, trip_style, notes
+    """
+    profile = {
+        "cuisines": None,
+        "interests": [],
+        "trip_style": None,
+        "notes": None,
+    }
+
+    try:
+        activity_interests = (
+            Activity.objects.filter(user=user)
+            .values("sport_type")
+            .annotate(count=Count("id"))
+            .exclude(sport_type__isnull=True)
+            .exclude(sport_type="")
+            .order_by("-count")[:5]
+        )
+
+        for activity in activity_interests:
+            sport = activity["sport_type"]
+            if sport:
+                interest = ACTIVITY_INTEREST_MAP.get(
+                    sport.lower(), sport.replace("_", " ")
+                )
+                if interest not in profile["interests"]:
+                    profile["interests"].append(interest)
+
+        category_interests = (
+            Location.objects.filter(user=user)
+            .values("category__name")
+            .annotate(count=Count("id"))
+            .exclude(category__name__isnull=True)
+            .exclude(category__name="")
+            .order_by("-count")[:5]
+        )
+
+        for category in category_interests:
+            category_name = category["category__name"]
+            if category_name and category_name.lower() not in [
+                i.lower() for i in profile["interests"]
+            ]:
+                profile["interests"].append(category_name)
+
+        top_lodging = (
+            Lodging.objects.filter(user=user)
+            .values("type")
+            .annotate(count=Count("id"))
+            .exclude(type__isnull=True)
+            .exclude(type="")
+            .order_by("-count")
+            .first()
+        )
+
+        if top_lodging and top_lodging["type"]:
+            lodging_type = top_lodging["type"].lower()
+            profile["trip_style"] = LODGING_STYLE_MAP.get(lodging_type, lodging_type)
+
+        top_regions = list(
+            VisitedRegion.objects.filter(user=user)
+            .values("region__name")
+            .annotate(count=Count("id"))
+            .exclude(region__name__isnull=True)
+            .order_by("-count")[:3]
+        )
+
+        if top_regions:
+            region_names = [r["region__name"] for r in top_regions if r["region__name"]]
+            if region_names:
+                profile["notes"] = f"Frequently visits: {', '.join(region_names)}"
+
+        if not profile["notes"]:
+            top_cities = list(
+                VisitedCity.objects.filter(user=user)
+                .values("city__name")
+                .annotate(count=Count("id"))
+                .exclude(city__name__isnull=True)
+                .order_by("-count")[:3]
+            )
+            if top_cities:
+                city_names = [c["city__name"] for c in top_cities if c["city__name"]]
+                if city_names:
+                    profile["notes"] = f"Frequently visits: {', '.join(city_names)}"
+
+        profile["interests"] = profile["interests"][:8]
+    except Exception as exc:
+        logger.error("Error building auto profile for user %s: %s", user.id, exc)
+
+    return profile
+
+
+def update_auto_preference_profile(user) -> UserRecommendationPreferenceProfile:
+    """
+    Build and save auto-learned profile to database.
+    Called automatically when chat starts.
+    """
+    auto_data = build_auto_preference_profile(user)
+
+    profile, created = UserRecommendationPreferenceProfile.objects.update_or_create(
+        user=user,
+        defaults={
+            "cuisines": auto_data["cuisines"],
+            "interests": auto_data["interests"],
+            "trip_style": auto_data["trip_style"],
+            "notes": auto_data["notes"],
+        },
+    )
+
+    logger.info(
+        "%s auto profile for user %s",
+        "Created" if created else "Updated",
+        user.id,
+    )
+    return profile