Add comprehensive TUI testing infrastructure (#10)

* Add comprehensive TUI testing infrastructure

- Create tui_app.rs to centralize UI state management
- Add tui_tests.rs with ratatui testing patterns
- Move UI logic from main.rs to tui_app module
- Update dependencies for testing support

This change improves testability by:
1. Isolating UI logic for better testing
2. Adding test infrastructure using ratatui patterns
3. Creating comprehensive test cases for UI components

Co-Authored-By: Yuta Hinokuma <[email protected]>

* fix test case sample

* Fix and refine TUI tests

Co-Authored-By: Yuta Hinokuma <[email protected]>

* fix: update TUI test assertions to match actual column headers

Co-Authored-By: Yuta Hinokuma <[email protected]>

* test: add clean operation test with dry-run verification

Co-Authored-By: Yuta Hinokuma <[email protected]>

* chore: update winnow dependency to v0.6.21

Co-Authored-By: Yuta Hinokuma <[email protected]>

* chore: update ratatui API usage for v0.29.0 compatibility

Co-Authored-By: Yuta Hinokuma <[email protected]>

* fix: restore cargo clean implementation in DeleteState::Confirm handler

Co-Authored-By: Yuta Hinokuma <[email protected]>

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Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Yuta Hinokuma <[email protected]>
Co-authored-by: Yuta Hinokuma <[email protected]>