Allow Microsoft account authentication via external system browser instead of embedded webview

[a012-alex]

Please confirm the following.

• I checked the existing issues for duplicate feature requests

What parts of Modrinth is your feature request related too?

Modrinth App

Is your suggested feature related to a problem? Please describe.

Currently, signing into a Microsoft/Minecraft account in Modrinth App uses an embedded webview popup. This requires users to re-enter their credentials every time, even if they are already logged into their Microsoft account in their primary system browser. Additionally, the embedded window limits access to browser-level capabilities such as password manager extensions, WebAuthn/passkey hardware keys, and auto-fill integrations.

Describe the solution you'd like

Provide an option (or default behavior) to authenticate Microsoft/Minecraft logins through the default system browser via OAuth/local callback server or deep-linking (modrinth://), similar to how Prism Launcher or HMCL handles authentication.

When initiated:

1. Modrinth App opens the OAuth login URL in the user's default system browser.
2. If already logged in, the user simply approves authorization without re-entering password/2FA.
3. The browser redirects back to Modrinth App to complete the token exchange.

Describe alternatives you've considered

Continuing to use the embedded webview window, which forces users to manually type passwords, 2FA codes, or re-authenticate through WebAuthn without browser extension support.

Additional context

UX/Efficiency: Users who maintain active Microsoft sessions in their browser can authorize Modrinth App with a single click.