Add configurable keyboard routing

[satoshi-assistant]

Summary

Adds configurable native keyboard routing for wxp-hosted WebViews.

• Adds WxpKeyboardRouting, WxpKeyboardKey, and WxpKeyboardDestination
• Supports WebView, Parent, and WebViewAndParent destinations
• Adds runtime updates via WxpWebView::set_keyboard_routing and WebViewDispatch::post_set_keyboard_routing
• Implements macOS routing in a small wkwebview/keyboard_routing.rs helper module
• Implements Windows routing in a small webview2/keyboard_routing.rs helper module
• Keeps product-specific timing decisions out of wxp; products can switch routing explicitly when their UI state changes

Why

Plugin hosts often reserve transport/global shortcuts such as Space, but WebView-based plugin UIs still need normal keyboard shortcuts and text input. A fixed “ignore all keys” strategy is too broad, and product-specific DOM focus heuristics do not belong in wxp. This adds a native routing primitive that products can configure and update intentionally.

The wry changes are split into helper modules so future upstream wry syncs have a smaller conflict surface.

Validation

• cargo fmt --package host_window --package novonotes_run_loop --package run_loop_test_utils --package run_loop_timer --package wxp -- --check
• cargo check --package wxp
• cargo check --package wxp --target x86_64-pc-windows-msvc
• cargo test --package wxp --lib

Manual validation still needed

Unit tests cover route-to-platform-code conversion, and CI covers 3OS compilation/tests. Actual host shortcut behavior still needs manual validation in plugin hosts/DAWs because tests cannot prove that a host consumes the forwarded native event as a transport shortcut.