Test Loop and dedicated Goal ownership on a real OpenCode host

[ByBrawe]

Goal

Prove the cross-plugin single-owner contract with the released dedicated Goal package on a real OpenCode host instead of only mocked Goal state.

Real-host canary

Adds scripts/host-goal-coexistence-canary.mjs and a dedicated Ubuntu/Windows CI lane that installs:

• current OpenCode CLI
• @bybrawe/opencode-goal@latest
• the current Loop plugin from this checkout

The canary creates one real OpenCode session, starts a real dedicated /goal, holds its first provider turn open, and then issues /loop devam et in the same session.

It requires:

• the released Goal package to persist an active same-session Goal snapshot
• Loop to emit goal-overlap-blocked
• no Loop job to be persisted
• no Loop autonomous provider request to start
• no command bridge request to leak to the model
• the dedicated Goal to remain active

The CI lane uses @bybrawe/opencode-goal@latest intentionally so scheduled CI also detects future companion releases that break the ownership contract.

No production Loop behavior changes in this PR; it locks the already-shipped 0.5.34 ownership guard to the actual companion package and OpenCode host.

[ByBrawe]

Superseded by #144. The original run used Goal 1.3.25 and pre-0.5.35 Loop code, so its provider-cancel/command-bridge behavior is historical evidence rather than current-release evidence. #144 re-runs the same real-host overlap probe from Loop 0.5.35 with Goal 1.3.26 pinned.