fix(ci): the bake tests that exercise the renderer run when the renderer changes

[apresmoi]

Why

Plan 4 / C2 moved renderer tests that import the bake into packages/bake. The CI selector (affected-tests.mts) joins the offline tools only when a tool changed, so on a renderer-only change those suites stopped running.

Re-including all of bake on a renderer change would restore them, but bake's whole suite is heavy and was deliberately excluded. Instead an explicit owner map, FOREIGN_TESTS, lists exactly the moved suites and the selector runs just those files when their owner (or a package it depends on) changed. A unit test guards the map: every entry must exist, sit in an offline tool and import its owner package.

What changed

• affected-tests.mts: FOREIGN_TESTS, a files result and a new test_files output; a file whose own package already runs is left to that package's glob.
• universe.yml: test_files is exported by changes, passed to the packages lane as CI_TEST_FILES and appended to the tests array; the lane is skipped only when both packages and files are empty.
• check-ci.mts: the local run substitutes the new output and the updated skip expression.
• CONTRIBUTING.md: the selector rule names the exception.

The 12 files are the 11 renderer tests moved by f309c5c (scientific-focus excluded: it runs in the integration lane, covered by the site lane) plus the prepared-volume-runtime test moved by 72803ea.

Checks

• Selector on a renderer-only diff (identical to the committed run):

  Packages to test: renderer; extra files: packages/bake/src/contract/feature-fixture.test.mts packages/bake/src/contract/object-runtime.test.mts packages/bake/src/contract/object-selection-runtime.test.mts packages/bake/src/contract/prepared-material.test.mts packages/bake/src/contract/renderer-navigable-object-mount.test.ts packages/bake/src/objects/layers/paged-ellipsoid/renderer-surface-target.test.ts packages/bake/src/presentation/renderer-depth-partitions.test.ts packages/bake/src/sky/renderer-parallax.test.ts packages/bake/src/stars/renderer-point-field-bank.test.ts packages/bake/src/stars/renderer-validation.test.ts packages/bake/src/volume-leaves/renderer-prepared-leaf-frustum.test.ts packages/bake/src/volume-leaves/renderer-prepared-volume-runtime.test.ts; site: true.
  

• The workflow's tests loop, run for real with CI_TEST_PACKAGES=renderer and the 12 files: the foreign files execute (87 tests, 0 fail).
• Files-only does not skip the packages lane; the workflow YAML parses.
• Mutation: replacing the owner filter with false fails 3 tests in affected-tests.test.mts; restored, all 6 pass.
• affected-tests.test.mts and check-ci.test.mts: 7 pass.
• eslint on .github/scripts, typecheck:scripts, documentation links (--base origin/main), architecture check and the commit-message range check pass.

See the PR rules.