chore: remove 20.7 MiB of duplicate and unused media (#20416)

* chore: remove duplicate and unused documentation media

* chore: guard README local links and refresh tile-01 vendor metadata

- Add config/scripts/check-readme-local-links.mjs: every local src/srcset/href
  in README.md and docs/readme/*.md must resolve to a tracked file. Runs in the
  ungated root_directory_guard job so docs-only diffs (which skip static_analysis)
  still catch a deleted docs-site or feature-wall asset the README embeds.
- Refresh tile-01.recorded-at.json to what vendor-feature-wall-assets.mjs now
  emits for the tab-split source path.
- Drop the pr-19217 evidence prose that cited the removed screenshots.

* fix: accept single-quoted attributes in README local link check

The parser only matched double-quoted src/srcset/href, so <img src='missing.gif'>
was skipped and the guard passed a README that GitHub renders with a broken image.
Regression test fails without the parser change.

.github/workflows/pr.yml

@@ -276,6 +276,12 @@ jobs:
           HEAD_SHA: ${{ github.event.pull_request.head.sha }}
         run: node .github/scripts/check-root-directory-entries.mjs "$BASE_SHA" "$HEAD_SHA"
 
+      # Why here: the READMEs embed media owned by docs/site and resources/onboarding,
+      # and the classifier skips static_analysis for docs-only diffs. This job runs
+      # on every PR and needs no install.
+      - name: Check README local links
+        run: node config/scripts/check-readme-local-links.mjs
+
   typecheck:
     needs: [code_paths]
     if: needs.code_paths.outputs.typecheck == 'true'