fix: add terminal refresh button

[Vishal-080]

Summary:

• Add a refresh button to the terminal toolbar.
• Refresh safely tears down and recreates the terminal mux.
• Tests cover the UI trigger and reconnect lifecycle.

Tests:

• npm --prefix frontend run test -- src/renderer/components/TerminalPane.test.tsx src/renderer/components/CenterPane.test.tsx src/renderer/hooks/useTerminalSession.test.tsx
• npm --prefix frontend run typecheck

[somewherelostt]

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• @illegalcall
• @Pulkit7070

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