Support custom provider quota visibility in the sidebar

### Problem / use case

The sidebar can currently show quota or usage information for logged-in Claude/Codex accounts. However, users may also have quota or plan limits from custom providers or provider-specific plans, for example GLM coding plans and other configured providers.

Those custom provider quotas are currently not visible in the same account/quota surface, so users have to track them outside Orca.

### Requested behavior

- Show quota/usage information not only for logged-in Claude/Codex accounts, but also for user-configured providers and custom plans where quota data is available.
- Support providers such as GLM coding plans and similar custom/provider-specific quotas.
- Make unsupported providers explicit in the UI when quota cannot be queried automatically.

### Why this matters

Users may rely on multiple providers with separate quota systems. A single sidebar/account view for both built-in accounts and custom provider plans would make it easier to understand remaining usage before starting sessions.