Add terminal history persistence

Terminal history is currently stored in-memory via TerminalBuffer class

• History should persist across task restarts and browser sessions
• Store terminal entries in database with task association for retrieval
• Update useTerminalSocket to handle persistent history loading

Start by tracing the in-memory history in TerminalBuffer and the loading flow in useTerminalSocket. Identify the database entry point and task association used by the terminal, then persist entries so they can be retrieved after task restarts and browser sessions. Done means history is restored for the associated task in both cases.

Written by the indexing model from the issue text.