test(loop): isolate installer gh dependency

[codeacme17]

Summary

• provide an executable fixture gh for the trusted-control-plane installer integration test
• prepend the fixture directory only for the installer subprocess
• assert the generated manifest binds the fixture executable

Review finding

Resolves accepted finding RVW-1-1-1 from Traviinam review #109 (review). PR #109 was merged at head e794f6a before this repair was committed.

Verification

• env PATH=/usr/bin:/bin /Users/leyoonafr/.nvm/versions/node/v24.5.0/bin/node --test loops/issue-dev-loop/tests/install-trusted-control-plane.test.mjs
• pnpm loop:issue-dev:test (87 tests passed)
• pnpm verify

Risk

Low. This changes only the installer integration-test fixture and removes dependence on a host-installed gh binary.

Owner controls Ready, approval, and merge.

[Traviinam]

PASS

Reviewed immutable diff 376f838..8edc975.

• Standards: PASS.
• Spec: PASS. The test creates an executable gh outside the fixture repository, prepends it only to the installer subprocess PATH, preserves access to real git, and asserts the manifest binds the fixture executable.
• Verification: restricted PATH=/usr/bin:/bin reproduction passed; loop suite passed 87/87. Reported full pnpm verify also passed.
• Prior finding: RVW-1-1-1 is resolved.
• Residual risk: full pnpm verify was not independently rerun during this review; the change is test-only and has no product, public API, Web Audio, React, accessibility, or package-runtime surface.

Reviewed head: 8edc975

Cycle-result digest marker: unavailable because PR #110 is a pre-activation bootstrap follow-up with no durable issue-loop run/result.