Feature: /clear should preserve session name

Summary

When using /clear to reset conversation history, the session name (title) is also cleared/reset. It would be better if /clear preserved the session name.

Current Behavior

1. Rename a session with /rename my-session
2. Run /clear
3. The session name is reset — the previous name is lost

Expected Behavior

/clear should only clear the conversation history and free up context, while keeping the session name intact.

Rationale

• The session name is a user-chosen identifier, not part of the conversation context
• Users often name sessions to organize their work (e.g., "feature-auth", "debug-api")
• After clearing context mid-task, the session name still describes what the user is working on
• Having to /rename again after every /clear is unnecessary friction

Suggested Solution

Option A (preferred): /clear preserves the session name by default.

Option B: Add a flag like /clear --keep-name or /clear --preserve-name to optionally preserve it.