Use the owned login WebView for first login too, not just add-account

The Chrome Custom Tab path for the first/only login had real costs -
no way to close it automatically on success, and it's a separate task
outside the app's own navigation - that only bought Chrome's own
autofill in exchange. LoginWebViewView now handles every login, not
just add-account, which was already using it to avoid a Custom Tab
silently reusing Chrome's session for a different account.

url_launcher is no longer a dependency as a result.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

android/app/src/main/AndroidManifest.xml

@@ -70,12 +70,6 @@
             <action android:name="android.intent.action.PROCESS_TEXT"/>
             <data android:mimeType="text/plain"/>
         </intent>
-        <!-- Needed so url_launcher can find a browser for Nextcloud Login Flow v2. -->
-        <intent>
-            <action android:name="android.intent.action.VIEW"/>
-            <category android:name="android.intent.category.BROWSABLE"/>
-            <data android:scheme="https"/>
-        </intent>
         <!-- Needed so open_file can find apps to open downloaded files. -->
         <intent>
             <action android:name="android.intent.action.VIEW"/>