feat(ui): add saved drafts support to chat window (#552)

[annukumar123]

Summary

Implements local draft persistence in ChatWindow for issue #552.

Changes

• Saves input draft to localStorage keyed by sessionId as user types.
• Automatically loads existing draft when switching sessions.
• Clears localStorage draft upon message submission.
• Added unit test suite covering initial render, typing persistence, cleanup on send, and session switching.

Closes #552

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[annukumar123]

@imDarshanGK
It is perfect . you can verify now