[Formulus] Fix: Clear token cache when switching servers

[najuna-brian]

Description

App bundle downloads fail with 401 errors when switching between servers because the cached authentication token from the previous server is reused.

Solution

• Clear cached token when server URL changes in getApi()
• Clear cached token on login to ensure fresh token for new server
• Added clearTokenCache() public method for explicit cache invalidation

Changes

• SynkronusApi.getApi(): Clear token cache when server URL changes
• SynkronusApi.clearTokenCache(): New public method to clear cached token
• Auth.login(): Clear token cache before logging in

Testing

• Login to local server → app bundle downloads successfully
• Switch to demo server → app bundle downloads successfully (no 401 errors)

Closes #111