feat: implement robust cookie matching, netscape import, and login flow fixes

[victoria-rose]

This PR ports the robust cookie and authentication fixes to resolve issues with session expiration (2-hour logout loops) and Google blocking the embedded sign-in window (insecure browser block).

Summary of Changes

1. Backend Cookie Domain Matching & Imports (Rust):

   • Implemented matching of .youtube.com\ wildcard domains to prevent cookie jar filtering (fixes session expiration/logouts).
   • Added \import_cookies_from_text\ Tauri command to parse and import Netscape HTTP Cookie File format.
   • Integrated
     fd\ file-open dialogs in Rust backend to select cookie files from disk.
   • Added \continue_login\ command to resume Tauri webview loop after user bypasses warnings.

2. Frontend Authentication Context Update:

   • Removed stale \�isitorData\ header from InnerTube requests when an authenticated context/cookie is active (prevents HTTP 401/404 errors).

3. Dedicated Account Settings Tab:

   • Created a separate Account tab in the Settings Dialog.
   • Moved login status and Sign In controls to this tab.
   • Added a file-selector and copy-paste text field under Settings -> Account to allow importing Netscape format cookies exported from the user's web browser.

4. Embedded WebView Polish:

   • Displays notifications and toast alerts when the browser encounters safety blocks or insecure states, with continue triggers.