#8135: Adding Groq as a model provider

Added groq as a model provider. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds Groq to the provider usage subsystem: it introduces a new `groq` `UsageProviderId`, adds a label, includes Groq in the default usage provider list, resolves a Groq API key from env/config/auth profiles, and wires a new `fetchGroqUsage` implementation into the usage summary loader. It also adds end-user docs linking Groq under the provider catalog. Main concern is that the usage fetch currently relies on a hard-coded `/openai/v1/usage` endpoint and treats any failure/parse issue as “no usage”, which may silently mislead users rather than indicating the feature is unsupported or unavailable. <h3>Confidence Score: 3/5</h3> - This PR is mostly safe to merge, but Groq usage reporting may be misleading due to an unverified endpoint and silent fallback behavior. - Changes are localized and type-safe (new provider ID, labels, auth resolution, and a fetch stub). The main risk is functional: `fetchGroqUsage` will likely return empty usage in many real-world cases, making the UI appear as if Groq has no usage rather than indicating unsupported/unavailable usage tracking. - src/infra/provider-usage.fetch.groq.ts, docs/providers/groq.md <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->