fix(chat): add saved AI defaults and harden suggestions

.memory/knowledge/domain/ai-configuration.md

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+# AI Configuration Domain
+
+## WS1 Configuration Infrastructure
+
+### WS1-F1: Instance-level env vars and key fallback
+- `settings.py`: `VOYAGE_AI_PROVIDER`, `VOYAGE_AI_MODEL`, `VOYAGE_AI_API_KEY`
+- `get_llm_api_key(user, provider)` falls back to instance key only when provider matches `VOYAGE_AI_PROVIDER`
+- Fallback chain: user key -> matching-provider instance key -> error
+- See [tech-stack.md](../tech-stack.md#server-side-env-vars-from-settingspy), [decisions.md](../../decisions.md#ws1-configuration-infrastructure-backend-review)
+
+### WS1-F2: UserAISettings model
+- `integrations/models.py`: `UserAISettings` (OneToOneField to user) with `preferred_provider` and `preferred_model`
+- Endpoint: `/api/integrations/ai-settings/` (upsert pattern)
+- Migration: `0008_useraisettings.py`
+
+### WS1-F3: Provider catalog enhancement
+- `get_provider_catalog(user=None)` adds `instance_configured` and `user_configured` booleans
+- User API keys prefetched once per request (no N+1)
+- `ChatProviderCatalogEntry` TypeScript type updated with both fields
+
+### Frontend Provider Selection (Fixed)
+- No longer hardcodes `selectedProvider = 'openai'`; auto-selects first usable provider
+- Filtered to configured+usable entries only (`available_for_chat && (user_configured || instance_configured)`)
+- Warning alert + Settings link when no providers configured
+- Model selection uses dropdown from `GET /api/chat/providers/{provider}/models/`
+
+## Known Frontend Gaps
+
+### Root Cause of User-Facing LLM Errors
+Three compounding issues (all resolved):
+1. ~~Hardcoded `'openai'` default~~ (fixed: auto-selects first usable)
+2. ~~No provider status feedback~~ (fixed: catalog fields consumed)
+3. ~~`UserAISettings.preferred_provider` never loaded~~ (fixed: Settings UI saves/loads DB defaults; chat initializes from saved prefs)
+4. `FIELD_ENCRYPTION_KEY` not set disables key storage (env-dependent)
+5. ~~TypeScript type missing fields~~ (fixed)
+
+## Key Edit Reference Points
+| Feature | File | Location |
+|---|---|---|
+| AI env vars | `backend/server/main/settings.py` | after `FIELD_ENCRYPTION_KEY` |
+| Fallback key | `backend/server/chat/llm_client.py` | `get_llm_api_key()` |
+| UserAISettings model | `backend/server/integrations/models.py` | after UserAPIKey |
+| Catalog user flags | `backend/server/chat/llm_client.py` | `get_provider_catalog()` |
+| Provider view | `backend/server/chat/views/__init__.py` | `ChatProviderCatalogViewSet` |