Present Point and Mouse as scanning modes

[enaboapps]

Closes #858.

Present Point and Mouse as the two primary scanning modes. Select resumes the last explicitly used mode across app restarts, defaulting to Point for older settings. Add Open Point as an additive switch action; the Mouse panel now switches directly to Point. The Scanning page explains both paths before shared and advanced settings.

Validation:

• Node 24: npm run lint, npm test, and npm run build passed (218 UI tests and 5 Node tests).
• Rust 1.97.1: cargo fmt --manifest-path src-tauri/Cargo.toml --check, cargo clippy --manifest-path src-tauri/Cargo.toml --all-targets -- -D warnings, and cargo test --manifest-path src-tauri/Cargo.toml passed (512 unit tests, 1 ignored, 7 integration tests).
• Windows 11 Parallels ARM64 VM: built the latest head 4cea753 with Node 24.19.0 and Rust 1.97.1 using npm run tauri -- build --debug --no-bundle --target aarch64-pc-windows-msvc. Tested native switch key press/release edges against ordinary Notepad windows: Select started Point, Open Mouse entered Mouse, Open Point returned to Point, and the Mouse panel's Switch to Point tile returned to Point. Escape stopped without changing the saved Mouse mode; after app restart, Select reopened Mouse. The pointer ring appeared in Mouse and cleared on Point/Stop. The native settings page displayed the two mode cards and the saved Select mode. Restored original VM configuration files byte-for-byte and left the corrected build running.
• VM limits: Parallels-generated key events exercised Windows switch capture but were not a separate physical switch device. The VM has one monitor, and no Android Remote was connected; monitor navigation and remote disconnect rely on automated tests.
• Independent review of 4cea753 found no actionable findings.
• Required PR CI passed on 4cea753: frontend (rerun after an unrelated switch-practice focus timing failure), dependency audit, macOS native, Windows native/NSIS and UI Access, CodeQL, and JavaScript/TypeScript analysis.

Follow-up review fixes (ddbd3ad, d14d0e1):

• Saving settings from the UI keeps the saved Point/Mouse mode, so an out-of-date UI config can no longer overwrite it. The config is merged and saved while holding the controller lock.
• All scanning settings saves replace the file safely: the new contents are written to a temp file, flushed to disk and then renamed over the old file, and the temp file is removed if anything fails. Before this, a write interrupted by a crash could corrupt the settings file, and the app would then quietly reset all scanning settings to defaults.
• If saving the mode fails, the switch action still runs. The mode is kept in memory and written with the next settings save.
• Rust 1.97.1: cargo fmt --check, cargo clippy --all-targets -- -D warnings and cargo test pass (514 unit tests, 1 ignored, 7 integration tests). Node 24: npm run lint and npm test pass (218 UI tests, 5 Node tests). The frontend is unchanged, so the build was not re-run. The Windows VM test has not been repeated on these commits.
• Independent review of latest head d14d0e1 found no actionable findings. Two points were accepted as-is: the mode is saved before its action runs, and the runtime paths that need an AppHandle have no tests.

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