refactor(repo): resolve changed-code audit

[jrusso1020]

What

Resolve all changed-code findings introduced by the refactoring stack.

Why

A large safety-oriented stack should not add dead code, avoidable complexity, or duplicated test and helper logic.

How

Reuse the shared auth fixture, centralize the Cloud Run FPS helper and Studio persistence prop type, and add narrow documented suppressions only for intentional migration/test-corpus repetition.

Test plan

• Fallow new-only gate: zero dead code, complexity, or duplication introduced
• Focused affected tests, full pre-commit checks, and complete stack-wide validation

[miguel-heygen]

Approved exact head ab8b50a. Audited: all 21 changed files and the complete incremental diff; trusting: none. Also read every current issue comment, review, REST comment, and GraphQL thread. The Cloud Run FPS extraction preserves validation, defaults, ordering, and command-specific errors; the shared auth fixture restores a safe superset of the prior env keys; the Studio persistence type is field-compatible; and the Fallow suppressions are category-scoped and documented around intentional lifecycle, migration, AST-walk, or test-corpus repetition. Exact-head required CI and the full applicable matrix are green. Non-blocking cleanup only: StudioRightPanelProps still redeclares the five fields inherited from StudioEditPersistenceProps, so the type centralization could be completed later without behavior impact. No blocking findings. — Magi