[Feat] Add OpenCode Go subscription support

[roomote-roomote]

Opened on behalf of Matt Rubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• added OpenCode Go as a distinct inference provider with opencode-go/... models and a dedicated OPENCODE_GO_API_KEY
• routed Go requests through the /zen/go/v1 upstream for chat completions, Responses, and Anthropic Messages APIs in both direct and inference-gateway modes
• limited Go suggestions to Roomote's central model catalog and configured the requested defaults: GLM 5.2 for coding, Luna for helper and vision, DeepSeek Flash for explore, MiniMax M3 for code review, and Qwen3.8 Max for planning/advisor
• added provider setup, Compose forwarding, runtime tests, and separate OpenCode Zen and Go documentation

Why this change was made

Roomote previously labeled its OpenCode integration as supporting both Zen and Go, but only configured Zen's provider ID and endpoint. OpenCode Go uses a separate provider namespace and subscription endpoint, so Go keys and models could not run correctly.

Impact

Operators can connect an OpenCode Go subscription independently from Zen and use its included allowance across Roomote task roles. Existing OpenCode Zen behavior and credentials remain unchanged. All Compose shapes validated; the broader deployment validator's unrelated Caddy adaptation step could not run because this sandbox does not expose a Docker socket.

[roomote-community]

No code issues found. See task

_{Reviewed b690768}