fix: recently added items sort order in the homepage

.ie. stop relying on folder last mod date, and use the latest file from the folder

+ bump watchdog to v4
+ add WIP docs (stashed in .github/code.docs for now)

.github/code.docs/playlists.md

@@ -0,0 +1,8 @@
+# Playlists
+
+Playlists are stored in the user data database. You can find the schema at `app/db/sqlite/queries.py`.
+
+The methods for manipulating playlists in the database can be found at `app/db/sqlite/playlists.py`.
+
+The api routes for playlists can be found at `app/api/playlist.py`.
+