The web-backend keeps its own playlist builder for the PWA URL-import
path, so the shared createPlaylistObject() DRM hook never ran there and
encrypted DASH channels imported by URL reached Shaka without keys.
Apply extractDrmFromRaw() in that builder too and cover the path with a
regression test.
Addresses Codex review on PR #1225.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>