[FEATURE]: add /clear slash command to clear conversation in the same session (similar to claude code)

[sdeonvacation]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Use Case

When working on a long session, the conversation history can become cluttered with irrelevant messages from previous tasks. Currently, users must create a new session to start using /new command
fresh, losing the session context.

The /clear command would allow users to:

• Clear all messages from the current session
• Keep the same session (preserving session ID, title, etc.)
• Start fresh without context from previous messages being sent to the model

Proposed Implementation

• Add a new slash command /clear in the TUI
• Delete all messages via the existing session.deleteMessage API
• Refresh the UI after deletion
• Show a toast confirming how many messages were cleared

Verification

Tested locally:

• Command appears in slash command menu
• Messages are deleted from database
• UI refreshes to show empty conversation
• New messages after /clear don't include old context

[dexterhere04]

I tried implementing this according to your proposal , see my pull request to check how it is.