[Feature] Manage chat history functionalities

[b-re-w]

Issue

• Implement chat history management so that each new chat automatically receives a generated name and all conversation data is stored in a database with platform‑specific integrations.

Add chat history management with auto-generated names and DB storage

• Entry point: Identify the module handling new chat creation (e.g., chat/service or conversations/controller) and add logic to generate a default chat title (timestamp or first message snippet).
• Persistence: Introduce a ChatHistoryRepository (e.g., under storage/ or persistence/) with platform-specific adapters for the chosen DBs (PostgreSQL, SQLite, etc.).
• APIs: Expose methods to save, fetch, and list conversations (saveChat, getChatById, listChatsForUser) across platforms.
• Integration: Wire the repository into the chat service so each message and metadata (title, timestamps, participants) is saved.
• Documentation & tests: Document DB configuration steps per platform and add unit tests for chat creation, retrieval, and listing.