Avoid requiring static API key for OAuth Login

[egenvall]

Background

The addition of #76 based on #32 works by taking prescedence over the anthropic_key in config.toml.
However, the main improvement of the OAuth flow with spacebot auth login is to avoid having a fixed API key set for anthropic.

Issue

If no anthropic_key is set in the conf, the LLM calls will fail with a poorly descriptive message unknown provider anthropic when the routing model is set to anthropic/..

Solution

Resolve the anthropic key provider in the model configuration so that it can use the OAuth token even if no configuration entry for anthropic_key is set.

Test

Prerequisites

spacebot auth login
[ ] Remove anthropic_key from config.toml prior to this PR
[ ] Bot will not respond and -f -d will show the unknown provider error
[ ] Check out PR & run in dev
[ ] Bot is now responsive

Considerations

Having no API Keys set at all currently hows a yellow warning banner in the web dashboard.

cc @Marenz

[Marenz]

This is the right approach — resolving the Anthropic provider at the LlmManager level with an explicit match on all four cases (static+oauth, static-only, oauth-only, neither) is much cleaner than always registering a provider with an empty key.

I had a workaround for the same issue in #84 but dropped it in favor of this. #84 now only has the MiniMax routing fix.

[egenvall]

This is the right approach — resolving the Anthropic provider at the LlmManager level with an explicit match on all four cases (static+oauth, static-only, oauth-only, neither) is much cleaner than always registering a provider with an empty key.

I had a workaround for the same issue in #84 but dropped it in favor of this. #84 now only has the MiniMax routing fix.

Nice, makes sense!

[Marenz]

LGTM