Add xAI/Grok OAuth support

[rluisr]

Add xAI/Grok OAuth support

Summary

Add first-class xAI/Grok OAuth authentication to VibeProxy using the bundled CLIProxyAPI --xai-login flow.

Changes

• Register xAI as an OAuth service and expose its accounts in Settings
• Launch the bundled CLIProxyAPI xAI login flow and clean up stale login processes
• Add provider enable/disable support while preserving existing OpenAI-compatible providers named xai
• Add the xAI/Grok service row, account controls, authentication messaging, and a template-compatible icon
• Keep the expanded Services list reachable by allowing the Settings form to scroll
• Document xAI/Grok support and add provider wiring coverage
• Add a pull request description template because the repository did not contain one

Testing

• swift test (9 tests passed)
• swift build
• git diff --check
• Confirmed the bundled CLIProxyAPI v7.2.86 exposes --xai-login
• Confirmed Grok models are listed through GET /v1/models on port 8317
• Confirmed grok-4.3 Chat Completions returns HTTP 200 with grok-ok
• Confirmed grok-4.3 Responses API returns HTTP 200 with grok-responses-ok
• Confirmed streaming Chat Completions returns HTTP 200, the expected content, and [DONE]

Checklist

• Tests pass locally
• Documentation is updated where needed
• No unrelated changes are included

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Decouple OAuth xAI from custom xai providers

When an existing config defines an openai-compatibility provider named xai, this toggle writes enabledProviders["xai"], the same key used by the Custom Providers row (provider.id) and by resolveConfigPath when it builds disabledCustomProviderIDs; turning off the new OAuth row therefore removes that API-key provider from the generated config. Please keep the OAuth provider state under a distinct key or otherwise avoid coupling it to preserved custom xai providers.

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