Worker protocol resolution

Chose explicit protocol and route-table precedence over provider-family fallback because mapping OpenAI-family traffic to Anthropic selects the wrong parser, while collapsing Codex to Chat Completions loses Responses semantics. Preserve explicit Gemini; map Anthropic→Anthropic, OpenAI/DeepSeek→OpenAI, and openai-codex always→openai-codex-responses; only protocol-less OpenCode and unknown providers default to Anthropic.