feat(core,app,android,ios): My List, synced, and New badges with new-episode rows

My List is a list of titles to watch later, kept in my-list.json by
title key (pstr-core::mylist) and synced as one list/<key> register per
title, so an add or a removal on one device reaches every other. A list
file that will not parse is never written over: changing the list is
refused instead. It is a filter, a row on the library, a button on the
banner and the title page, and an entry in each tile's menu.

pstr-core::news reads node_first_seen against each share's first crawl,
so a newly added share does not badge its whole library. A title that
arrived in the last two weeks and was never played is New; a series
being watched counts the unwatched episodes that arrived after it was
last played ("3 new"). They fill the tile badge and the "New episodes"
and "Recently added" rows. shelves::home puts every row in one order
for all three apps, and a shelf tile of an airing show shows a
countdown ("Ep 8 · in 2 d").

The bridge gains TitleRecord.on_list and .badge, set_on_list, the
MyList filter, airing_countdown and SyncRecord.list_changed.

docs/ACCOUNT_AND_SYNC.md

@@ -4,8 +4,8 @@ Signing in to Proton is optional. Without it, the app plays public share links a
 everything on one device. Signing in adds two things:
 
 - **Folders of your own Drive** as shares, with no link to copy.
-- **Sync** of your place in every episode, your shares and your settings, across every device
-  you sign in on.
+- **Sync** of your place in every episode, your shares, your settings and My List, across every
+  device you sign in on.
 
 ## Signing in
 
@@ -51,6 +51,8 @@ When you are signed in, each device keeps a small file in your Drive. You find t
   your Drive)
 - Settings: playback, appearance and posters and descriptions, including a TMDB key
 - Matches you picked by hand, and your audio and subtitle choice for each show
+- My List: a title you add on one device is on the list of every other, and one you remove is
+  removed from all of them
 
 **What stays on each device:** volume and mute, the streaming cache size, text size, Wi-Fi only,
 background audio, hardware decoding, window size, and the library's filter and sort order.
@@ -60,7 +62,7 @@ and when it closes. **Sync now** runs it at once. Android also syncs in the back
 after you leave the app.
 
 **How conflicts are settled:** each device writes only its own file, and reads everyone else's.
-For each episode and each setting, the newest change wins. A device that signs in for the first
+For each episode, each setting and each title on My List, the newest change wins. A device that signs in for the first
 time takes the others' state and does not overwrite it with its own defaults.
 
 A device that has not synced for 90 days has its file moved to the Drive trash.