docs: Add /title and /rename commands to TUI mode documentation

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Summary

The /title slash command and its /rename alias (added in PR #11235) are not documented in the CLI TUI mode documentation.

Current State

The slash commands table in docs/cli/tui-mode.mdx lists available commands but is missing:

• /title - Set/change the title of the current session
• /rename - Alias for /title

Suggested Changes

Update the slash commands table in docs/cli/tui-mode.mdx to include:

Command	What it does
/title	Set or change the current session's title
/rename	Alias for /title

Reference

• Implementation PR: feat: alias /rename for /title #11235
• Code reference: extensions/cli/src/slashCommands.ts

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Co-Authored-By: Continue noreply@continue.dev
Co-authored-by: bekahhw rhawrot@gmail.com