feat(auth): adapt web multi session approach [AI]

[mbeernut]

Multi-account support (FEATURE_MULTI_ACCOUNT)

• Token refresh with account context — replaced library refreshToken() call with a direct JSON fetch to pass marketplaceAccountId to the Auth0 Action; the library silently drops additionalParameters so a custom fetch was the only option
• Feature flag stability — added an early return for fullVersion === '' in featureFlagsService to prevent the flag from falsely disabling during portal version loading
• Legacy account sync — added useLegacyAccountSync hook: when the feature flag is off, detects web-side account changes by watching the JWT accountId claim after each token refresh and invalidates userData/spotlightData queries accordingly
• Account switcher visibility fix — AccountToolbarButton now falls back to userAccountsData keyed by currentAccountId when userData?.currentAccount is null (loading or post-switch query clear), keeping the avatar visible and the button tappable
• Account list data fix — useUserAccountsData was calling getAccountsForUser (?select=groups,audit, no display fields) instead of getUserAccountsData (?select=id,name,icon,...); accounts now load with all fields needed for the list and toolbar avatar
• Repeated-switch guard fix — ProfileScreen initialises selectedAccountId from currentAccountId and uses selectedAccountId ?? currentAccountId in the guard, preventing no-op switches when the account ID is still loading on first render