fix: final review findings — env template placeholder, a11y live region, stale read-only comments

backend/library.py

@@ -1,7 +1,8 @@
 """The video archive, read as `<video_root>/<date>/<batch>.<ext>` (REQ-010…012).
 
-Read-only by construction: this module only ever lists and stats files, never
-writes into the user's recordings (REQ-074).
+Reads the archive and appends user-initiated uploads and date folders
+(REQ-178); nothing that exists is ever moved, renamed or deleted
+(REQ-163/074 as revised).
 """
 
 import os