🤖 Add vim toggle command and new Vim edits

[ammar-agent]

Summary

• add /vim slash command that toggles the global vim preference via persisted state
• gate VimTextArea behaviors behind the persisted toggle and reset when disabled
• implement vim 's' and '~' actions with integration tests
• allow updatePersistedState to accept functional updaters to avoid race conditions

Testing

• make lint
• make typecheck
• make test

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