fix(microsoft-shared): force prompt=consent on authorize URL

Without prompt=consent Microsoft may silently reuse a prior user consent
that doesn't include our new shared-mailbox scopes (Mail.ReadWrite.Shared,
Mail.Send.Shared). The result is a successful OAuth round-trip but an
access token missing the scopes, leading to 403 on the Graph access check
in the callback. Mirror the existing microsoft provider which sets the
same flag.

app/controllers/api/v1/accounts/microsoft_shared/authorizations_controller.rb

@@ -8,7 +8,8 @@ class Api::V1::Accounts::MicrosoftShared::AuthorizationsController < Api::V1::Ac
     redirect_url = microsoft_shared_client.auth_code.authorize_url(
       redirect_uri: "#{base_url}/microsoft_shared/callback",
       scope: microsoft_shared_scope,
-      state: encode_microsoft_shared_state(Current.account, upn)
+      state: encode_microsoft_shared_state(Current.account, upn),
+      prompt: 'consent'
     )
 
     if redirect_url