fix(macos): opt out of Writing Tools to prevent Campo crash (#355)

[nvkvin]

Summary

On macOS 15.1+ (Sequoia / Tahoe 26+), AppKit's CampoLightweightUI subsystem detects mouse dwelling over text selections to show floating Apple Intelligence Writing Tools affordances.
When inspecting or attaching to WKWebView text selections, an internal AppKit assertion fails (*** Assertion failure in <private>, NSCampoLightweightUIController.m:1429), throwing an NSInternalInconsistencyException inside Cocoa's event loop (-[NSApplication sendEvent:]).
Because Tauri's tao hooks sendEvent: via an extern "C" Rust callback without unwinding support, the uncaught exception hitting the FFI boundary causes Rust's runtime to trigger panic_cannot_unwind, terminating the process with SIGABRT ("Abort trap: 6").

This PR opts out of Writing Tools on macOS by setting writingToolsBehavior = -1 (NSWritingToolsBehaviorNone) on WKWebViewConfiguration before the webviews are initialized.

Changes

• Configured WKWebViewConfiguration with setWritingToolsBehavior: -1 via without_writing_tools in src-tauri/src/lib.rs for both profile windows and the activity monitor window.
• Wrapped with #[cfg(target_os = "macos")] and added a compile-time no-op pass-through for #[cfg(not(target_os = "macos"))], ensuring zero impact on Windows and Linux builds.
• Added macOS-only dependency objc2-web-kit with the WKWebViewConfiguration feature in src-tauri/Cargo.toml.
• Added unit test test_writing_tools_behavior_opt_out asserting writingToolsBehavior is set to -1 on supported macOS runtimes.

Verification

• Manual testing: Exercised by hand on macOS 27.0.1 (26A434).
  Focused input fields and selected text, then repeatedly switched back and forth across applications with Cmd+Tab while resting the cursor over the text.
  Confirmed that Termic remains fully stable without crashes, dwelling triggers no Campo assertion failures, and right-clicking selected text cleanly omits Writing Tools affordances.
• cargo test --workspace --lib: 1,354 lib tests, 85 cli tests, and 21 proto tests passed.
• npm test: All 206 test files and 3,281 tests passed.
• npm run build: Passed cleanly with zero TypeScript or Vite bundle errors.

Closes #355

[simion]

Thanks for tracking this down, good catch on the per-window Writing Tools disable.

[simion]

Nit: NSWritingToolsBehaviorNone is used as a raw -1 literal in two places, a named constant would read better.

[simion]

— Simion's agent here, he'll take a look at this shortly.