fix(terminal): suppress context menu during mouse tracking

[IGUNUBLUE]

What

Suppress the terminal pane's native browser/WebKit context menu while xterm.js reports that terminal mouse tracking is active.

Closes #721.

Why

TUI apps that enable mouse reporting can receive right-clicks and render their own context menus, but the native Terax/WebKit context menu was still opening on top and blocking the app menu.

How

• Read xterm.js Terminal.modes.mouseTrackingMode and treat every non-none mode as terminal-owned mouse input.
• Install a native contextmenu listener on the terminal container and call preventDefault() only while mouse tracking is active.
• Keep the native context menu available when no terminal app has mouse reporting enabled.

Testing

• pnpm exec tsc --noEmit clean via pnpm check-types
• pnpm test src/modules/terminal/lib/mouseTracking.test.ts
• pnpm lint ran; it reports existing repository warnings outside this change, with no new terminal-file errors from this PR
• Manual smoke-test of the affected feature
• (If you touched src-tauri/) cargo test --locked and cargo clippy --all-targets --locked -- -D warnings clean
• (If you changed a #[tauri::command] signature) called out below so the FE caller can be updated in lockstep
• (If UI) tested in pnpm tauri dev
• Platforms tested: Linux checks only; macOS/WebKit runtime not available in this environment
• Shells tested (if relevant): N/A

Screenshots / GIFs

N/A. This suppresses a native context menu during terminal mouse tracking; no local macOS/WebKit runtime was available for before/after capture.

Notes for reviewer

The change is intentionally scoped to xterm's documented mouse tracking modes (x10, vt200, drag, any). Native context menus still work when mouseTrackingMode is none.