feat(tui): add mouse navigation support

[RaviTharuma]

Summary

• enable mouse capture while the TUI is active and restore the terminal cleanly on exit
• support wheel navigation, click-to-select, and clicking the selected result to open it
• map clicks through rendered list rows so grouped and detailed result layouts select the correct entry

Closes #7.

Checks

• cargo fmt --check (validated with rustfmt; the rustup cargo-fmt component is unavailable locally)
• cargo clippy -- -D warnings
• cargo test tui::tests (21 passed)
• cargo test (65 passed; 2 pre-existing app tests fail because their fixture expects HERDR_NAVIGATOR_LAUNCH_WORKSPACE_ID)

🤖 Generated with Claude Code

[RaviTharuma]

Primary issue: #7 (also supersedes closed duplicate #8).