IAV-1416/feat(teams-oauth): expose app display name and fallback resolve via client_credentials
- Add appDisplayName (app_displayname JWT claim) to MicrosoftTeamsTokenValidationResponse, OAuthTestStatusResponse, and OAuthStateStore OAuthResult.
- OAuthServiceImpl: capture app_displayname from delegated token when present; otherwise resolve it by fetching a client_credentials token and decoding its JWT payload (no Graph calls).