Add HyperFrames skills

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011h6NB8JQtfPc6eRCefEzBB

.agents/skills/faceless-explainer/scripts/lib/bgm-volume.mjs

@@ -0,0 +1,4 @@
+// Music sits under narration; a silent film brings music forward.
+export const BGM_BED_VOLUME = 0.12;
+export const BGM_SILENT_VOLUME = 0.9;
+export const bgmDefaultVolume = (hasVoice) => (hasVoice ? BGM_BED_VOLUME : BGM_SILENT_VOLUME);