[codex] Add multi-repo HTTP MCP and Kubernetes operator

[bigsmartben]

Summary

This PR packages the multi-repo CodeGraph work into one upstream review branch from the fork.

• Adds streamable HTTP MCP server support and gateway behavior for large multi-repository deployments.
• Adds repo-routed HTTP MCP tooling so one stable tool set can dispatch by repoId instead of expanding one tool namespace per repository.
• Adds the Kubernetes operator implementation for CodeGraphRepository and CodeGraphGateway, including CRDs, controllers, resource builders, runtime image wiring, samples, and docs.
• Updates README/site guidance, changelog notes, and MCP/gateway tests for the cloud-native and large-repo workflows.

Validation

• npm run build
• npm test
• npx vitest run __tests__/mcp-gateway.test.ts __tests__/mcp-http.test.ts __tests__/mcp-tool-allowlist.test.ts
• Not run here: go test ./... under deploy/operator because the current Windows environment does not have the go command installed.

Notes

The branch is intentionally sourced from the fork as bigsmartben:codex/multi-repo-http-mcp-k8s and targets colbymchenry/codegraph:main.