Fix CI: title removal order, Windows fixtures and POSIX-only tests

- Title removal ran the Steam shortcut tidy-up before steamos-delete, which
  finds the Proton prefix through that shortcut, so compatdata was left behind
  (e2e caught it). steamos-delete runs first again; art/collection tidy-up after.
- Test fixtures are byte-exact: never convert line endings (a text-looking
  fixture APK got CRLF on Windows and failed its SHA-256).
- Read index.html/artwork-settings.js as UTF-8 in tests; app-data backup and
  OBB shell tests run only on POSIX (they exercise the Frame-side scripts).
- e2e expects the icon under artwork/ now.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.gitattributes

@@ -6,3 +6,8 @@
 *.json text eol=lf
 *.md text eol=lf
 *.bat text eol=crlf
+# Test fixtures are byte-exact (hashes, signatures): never convert line endings.
+tests/fixtures/** -text
+*.apk binary
+*.jar binary
+*.obb binary