feat(reactor-cli): add OrcaRouter as a named built-in provider

[XiaoHuo888-hue]

This adds a dedicated OrcaRouter provider rather than relying on the generic OpenAI-compatible endpoint, mirroring how this repo already treats openrouter-style aggregators. Named routers such as orcarouter/auto pick an upstream per request. OrcaRouter is an OpenAI-compatible gateway that exposes 150+ models behind one API key, and it also provides gateway-level security controls for AI agents.

I'm an engineer on the OrcaRouter team.

What & why

packages/reactor-cli's KNOWN_PROVIDERS registry documents its extension mechanism ("Add a row as new vendors are asked for in the wild"). This PR adds one row for orcarouter:

• baseURL: https://api.orcarouter.ai/v1
• apiKeyEnv: ORCAROUTER_API_KEY

so a reactor.yml with model.provider: orcarouter resolves the OrcaRouter gateway base URL + key env through the exact same openai-compat (Chat Completions) path the existing openrouter / openai / google built-ins use — buildLiveProvider injects a scoped OpenAIProvider with useResponses: false, unchanged.

Changes

• src/model/provider-plan.ts — add orcarouter to KNOWN_PROVIDERS (base URL + key env)
• src/commands/init.ts — scaffold reactor.yml comment lists orcarouter + ORCAROUTER_API_KEY
• src/config.ts — base_url docstring lists orcarouter
• README.md — built-in provider list includes orcarouter
• src/__tests__/provider-plan.test.ts — new unit test asserting the orcarouter plan

Verification

• pnpm --filter @openprose/reactor-cli typecheck — clean
• pnpm --filter @openprose/reactor-cli build:test — clean
• provider-plan suite: 10/10 pass (baseline 9/9 + new orcarouter test)
• Full node --test over dist-test: 210 pass / 1 fail — the single failure is the contract-images symlink-cycle test on Windows (EPERM: operation not permitted, symlink), a pre-existing platform limitation unrelated to this change
• L3 live with a real OrcaRouter key: resolveProviderPlan({ provider: 'orcarouter' }) → https://api.orcarouter.ai/v1 + ORCAROUTER_API_KEY; reactor doctor --live smoke render OK (model anthropic/claude-haiku-4.5, 38 tokens); a structured render + function tool through the gateway returned 1872 tokens
• reactor init scaffold → reactor.yml documents the orcarouter provider; doctor recognizes ORCAROUTER_API_KEY

Notes

No behavior change for existing users: openrouter remains the default, and the SDK's lazy default-OpenRouter path is untouched (custom: true only for non-default providers).