Add OAuth / subscription-based API authentication

Please add an OAuth flow (or equivalent) that lets Pro+, Max, and other subscription users authenticate third-party apps using their existing Venice login — without generating or pasting a separate API key. Platforms like ChatGPT, Claude Max, and Grok already offer this. Third-party apps (e.g., Hermes Agent, Open WebUI, AnythingLLM, etc.) let users click "Log in with Venice" and immediately access their bundled API credits. This removes friction:

• No copy-pasting API keys

• No risk of leaking a long-lived key into app configs

• Subscribers can use their bundled credits in third-party tools without realizing they're "spending API"

• Easier onboarding for non-technical users