ci: a test-only change under studio or player needs no captures

[miguel-heygen]

What

The Studio and player captures check (scripts/check-pr-captures.mjs) asked for Before and After screenshots on PRs that only change tests under packages/studio or packages/player. It already skipped markdown there as "docs, not behaviour"; tests are the same kind of file. Paths under a tests/ or __tests__/ directory and files named *.test.* or *.spec.* are no longer watched, so a test-only diff passes with nothing to show, and a test file no longer spends the "No visible change" line budget.

Why

#4953 changes only the edit accuracy bench harness (packages/studio/tests/e2e/edit-accuracy/). The check counted its 44 lines as a Studio change and failed it, although nothing a user sees changes.

Related work

Refs #4953.

How

One test-path pattern next to DOC_FILE, applied in isWatched, the single filter every diffed path goes through (parseNumstat). The old TEST_FILE pattern only exempted *.test|spec.[jt]sx? from the visual-file rule (it missed .mjs and the tests/ tree); it goes, since a test path never reaches that rule now. The existing case that passed a .test.tsx straight to evaluate now goes through parseNumstat, as real runs do.

Test plan

• New case "test files under a watched package need no capture": a bench .mjs under tests/, a .spec.tsx and a .test.ts are filtered out and an empty body passes. Fails on main (all four files kept), passes here.
• node --test scripts/check-pr-captures.test.mjs: 75 pass, 0 fail, 3 runs in a row.
• The script against test(studio): the edit accuracy bench uses the port its server bound #4953's real diff with an empty body: main asks for Before and After; this branch passes.

No visible change

CI script only.

Size

One pattern and one test case.

[github-actions]

Edit accuracy: accurate 1216 (base branch 1216), smooth 1108 of those

The gate passes.
Smoothness is reported in the artifact, not gated. A case fails only if it fails 2 of 3 runs.

Quarantined, measured but not gated (1)

• seqnudge-none-pct-r0-nested-z100 (fixed by fix(studio): playhead keyframe edits keep their ease, undo names its edit and never waits on videos #4889): pass, passes

[terencecho]

Approved at 67a14da3aaee189e3b663f9ef1c03a689106f68a on code merit. The captures gate now excludes nested test/spec files and Markdown from the watched Studio/player diff before applying the visual-change and media rules; a mixed test-plus-production diff still enforces those rules. The added tests cover nested bench/test paths, Markdown, and the mixed production case, while existing visual rejection remains tested. I checked the exact-head script and workflow wiring; all 11 required checks passed, including captures and test reachability. I reviewed source via the GitHub API and did not run local tests.

— Review by tai (pr-review)