Classic-UI view: `_add_identity` path is unreachable (`_provider_names` returns configured providers, not the user's identities)

[ericof]

In AuthomaticView.__call__ (browser/view.py), an authenticated user visiting a configured provider always hits:

if not self.is_anon:
    if provider in self._provider_names:
        return self._redirect()

_provider_names returns the configured providers (self.config.keys()), and provider has already been validated against cfg earlier in __call__, so provider in self._provider_names is always true here. As a result the code never reaches the _add_identity branch further down — the "add a provider identity to an existing, logged-in account" feature is effectively dead via this view, and view.py lines ~135/151 are unreachable (surfaced while raising coverage to 97% in #112).

The check most likely intended to compare against the current user's already-connected identities, not the configured providers.

Suggested fix

• Add a method returning the logged-in user's connected provider names (from the plugin's UserIdentities), and gate the early redirect on that instead of _provider_names.
• Add a test covering the authenticated "add identity" flow once reachable.

Found during PR #115.