Add per-tab model persistence and selection functionality

[ferenci84]

Description

This PR adds per-tab model persistence and selection functionality. The changes enable each tab to remember and restore its selected AI model when switching between tabs. This improves the user experience by allowing users to maintain different model selections for different conversations.

Key changes:

• Added modelTitle property to Tab interface to store the selected model per tab
• Implemented setTabModel action in tabsSlice to update a tab's model title
• Enhanced tab creation to include the currently selected model
• Added functionality to restore the model when switching to a tab

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Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

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Tests

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Summary by cubic

Remember and restore the selected model per tab so each conversation can use its own model. Switching tabs now updates the global selection to match the tab’s saved model.

• New Features
  • Added modelTitle to Tab and a setTabModel reducer to store the model per tab.
  • New tabs inherit the current model; switching tabs restores that tab’s model via updateSelectedModelByRole.
  • Persist model changes into the active tab with a TabBar effect.