feat: replace provider-specific AI clients with unified callProvider()
- Remove callGemini() / callOpenAI() and all Gemini/OpenAI-specific env
vars (GoogleAPIKey, GeminiModel, OpenAIAPIKey, OpenAIBaseUrl, OpenAIModel)
- Add callProvider() supporting three API formats:
openai → POST /v1/chat/completions
responses → POST /v1/responses
anthropic → POST /v1/messages (x-api-key, anthropic-version header)
- New env vars: AI_BASE_URL, AI_API_KEY, AI_API_FORMAT, AI_MODEL
- Optional fallback provider via AI_FALLBACK_* (all four or none);
primary retries 3×, fallback attempts 1×
- Update wrangler.toml.example* to new var schema (default: Gemini OpenAI-compat)
- Update README, README_CN, AGENTS.md, CLAUDE.md accordingly
TooonyChen
c0e838b780