refactor(electron): replace webview with iframe and bump to v2026.4.110}
- Replace deprecated Electron <webview> tag with <iframe> and a WebviewProxy shim class that provides a compatible API (reload, goBack, goForward, zoom, navigation tracking) - Strip X-Frame-Options and CSP frame-ancestors headers in main process to allow OneNote to load inside iframe - Move Accept-Language header override and popup handler from webview attach events to main window webContents - Refactor event handler to use parent webContents frame events (did-frame-navigate, did-navigate-in-page, did-frame-finish-load) instead of webview DOM events - Update dark mode invert injection to use getIframeFrame() helper instead of webContents.fromId() - Simplify proxy and session access to use remote.getCurrentWebContents() instead of webview webContents lookup - Use local `win` variable instead of repeated `global.p3x.onenote.window.onenote` references - Remove commented-out code blocks and dead code in window creation - Disable nodeIntegrationInSubFrames and remove webviewTag from webPreferences - Remove electron from dependencies (keep in devDependencies only) - Delete AGENTS.md - Add changelog entries for v2026.4.109 and v2026.4.110 - Bump version to 2026.4.110 across package.json, README, changelogs, and artifacts