feat(app): add global favourite / toggle models functionality

[anduimagui]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This adds two related model-switching improvements in the app.

First, users can mark models as favorites directly in both model picker dialogs. Those favorites are persisted and can be cycled from the session commands.

Second, Settings > Models now includes a Quick Switch section where users choose two enabled models explicitly. The quick switch commands then toggle between that configured pair, and there is also a command to open the Quick Switch settings directly.

These changes work because model preferences are now persisted in the app model state, the quick-switch pair is validated against enabled models, and the session commands resolve the current selection against that stored configuration.

How did you verify your code works?

• bun run --cwd packages/app typecheck
• bun run --cwd packages/app test

Screenshots / recordings

Not included.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[rekram1-node]

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