Install script improvements:
- Show release notes after --update completes
- Detect installed version from backend/cmd/server/main.go
- Fetch releases from GitHub API and display changes between versions
- Graceful fallback when jq not installed (shows link only)
Embedding model detection:
- Add EMBEDDING_MODEL_PATTERNS for detecting embedding models
- Add embeddingModels and hasEmbeddingModel derived properties
- KnowledgeTab shows embedding model status conditionally
- MemoryTab shows model installation status with three states