feat: add Venice AI provider integration

Venice AI is a privacy-focused AI inference provider with support for
uncensored models and access to major proprietary models via their
anonymized proxy.

This integration adds:

- Complete model catalog with 25 models:
  - 15 private models (Llama, Qwen, DeepSeek, Venice Uncensored, etc.)
  - 10 anonymized models (Claude, GPT-5.2, Gemini, Grok, Kimi, MiniMax)
- Auto-discovery from Venice API with fallback to static catalog
- VENICE_API_KEY environment variable support
- Interactive onboarding via 'venice-api-key' auth choice
- Model selection prompt showing all available Venice models
- Provider auto-registration when API key is detected
- Comprehensive documentation covering:
  - Privacy modes (private vs anonymized)
  - All 25 models with context windows and features
  - Streaming, function calling, and vision support
  - Model selection recommendations

Privacy modes:
- Private: Fully private, no logging (open-source models)
- Anonymized: Proxied through Venice (proprietary models)

Default model: venice/llama-3.3-70b (good balance of capability + privacy)
Venice API: https://api.venice.ai/api/v1 (OpenAI-compatible)

src/commands/auth-choice.preferred-provider.ts

@@ -19,6 +19,7 @@ const PREFERRED_PROVIDER_BY_AUTH_CHOICE: Partial<Record<AuthChoice, string>> = {
   "google-gemini-cli": "google-gemini-cli",
   "zai-api-key": "zai",
   "synthetic-api-key": "synthetic",
+  "venice-api-key": "venice",
   "github-copilot": "github-copilot",
   "copilot-proxy": "copilot-proxy",
   "minimax-cloud": "minimax",