refactor(renderer): replace AngularJS with vanilla JS and migrate to ESM}
- Replace AngularJS and Angular Material with vanilla JavaScript using native <dialog> elements for prompts and custom CSS toasts - Migrate all renderer-side .js files to .mjs (ESM) with import/export syntax, using a CJS shim (shim.js) for Electron API access - Remove 6 dependencies: angular, angular-animate, angular-aria, angular-material, angular-messages, @fontsource/roboto - Delete AngularJS bootstrapping (angular.js), prompt dialog (angular/prompt/index.js), and toast service (angular/toast/index.js) - Add new ui.mjs module with vanilla JS toolbar, prompt dialogs, and toast notifications - Rewrite event/handler.mjs and ipc/handler.mjs for ESM compatibility - Rewrite load.mjs with vanilla JS initialization replacing Angular bootstrap and $rootScope bindings - Restyle bottom toolbar with OneNote-branded purple (#7719AA) theme and system font stack (Segoe UI / Noto Sans / Liberation Sans) - Expand style.css with vanilla dialog/toast styles replacing Angular Material CSS - Remove unused remove-cookies.js utility - Update index.html to load ESM modules and remove Angular directives - Bump version from 2026.4.105 to 2026.4.106