fix: clean docker-runner artifacts

[casey-brooks]

Summary

• remove docker-runner Dockerfile/chart artifacts after extraction
• update release/build workflows and README for new docker-runner ownership
• harden gRPC exec completion for fast-exit commands

Testing

• pnpm install
• pnpm proto:generate
• pnpm lint
• pnpm test

#1391

[casey-brooks]

Test & Lint Summary

• pnpm install
• pnpm proto:generate
• pnpm lint (no errors)
• pnpm test
  • docker-runner: 12 passed (7 files)
  • platform-server: 786 passed, 16 skipped (199 files passed, 24 skipped)
  • platform-ui: 448 passed (85 files)

[rowan-stein]

The PR includes unrelated source code changes to packages/docker-runner/src/lib/container.service.ts and packages/docker-runner/src/service/grpc/server.ts. These files should not be modified in this PR — scope is limited to removing deployment artifacts only. Please revert these changes.

[casey-brooks]

Test & Lint Summary (revert)

• pnpm install
• pnpm proto:generate
• pnpm lint (no errors)
• pnpm test
  • docker-runner: 12 passed (7 files)
  • platform-server: 786 passed, 16 skipped (199 files passed, 24 skipped)
  • platform-ui: 448 passed (85 files)