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.

docs/USER_GUIDE.md

@@ -14,16 +14,22 @@ The library shows every title from every share in one place. Two shares that hol
 show it once.
 
 - **The banner** across the top shows the title you watched last first, with **Resume**, how far
-  into it you are and **More info**. It then turns through up to four more titles that have a wide
+  into it you are, **More info** and **My List**. It then turns through up to four more titles that have a wide
   picture, a different set each day, moving on every eight seconds. It holds still while the
   pointer is over it; on a phone, swipe it or tap a dot under it to move on yourself. Its shading
   takes on the colours of the picture behind it, and so does the top of a title's page.
 - **Continue watching** has the episode you stopped in for each show, or the next one when you
   finished an episode. To take a show off this row, right-click it and choose **Remove from
   Continue watching**.
+- **New episodes** has the shows you are watching that got episodes since you last watched them.
+  Their tiles say how many, for example **3 new**.
+- **My List** has the titles you put aside to watch, the last one added first.
+- **Recently added** has the titles that arrived in the last two weeks and that you have not
+  started. Their tiles say **New**. What was already there when you added a share is not new.
 - **Shelves** such as **Airing now**, **Directed by Satoshi Kon** or **From MADHOUSE** appear when
   posters and descriptions are on. The app shows at most four, and only for a director, studio or
-  genre with at least three titles.
+  genre with at least three titles. On a shelf, a show that is still airing says when its next
+  episode is out, for example **Ep 8 · in 2 d**.
 - **All titles** is the full grid. Choose a filter and a sort order above it.
 
 Rows that run past the window fade out at the edge. Point at a row to show the arrows at its
@@ -31,7 +37,12 @@ ends, which move it along by a page.
 
 | Filters | Sort orders |
 |---|---|
-| All, Series, Films, Watching, Not started, Downloaded | A – Z, Recently watched, Recently added, Newest, Highest rated, Most popular |
+| All, My List, Series, Films, Watching, Not started, Downloaded | A – Z, Recently watched, Recently added, Newest, Highest rated, Most popular |
+
+**My List** is a list of titles to watch later. Add a title with **My List** on its page or on
+the banner, or right-click its tile and choose **Add to My List**. Choose the button again, or
+**Remove from My List**, to take it off. When you are signed in, the list syncs to your other
+devices ([Account and sync](ACCOUNT_AND_SYNC.md)).
 
 **Group franchises** folds a series, its sequels and its films into one tile with a **+N** badge.
 It is on by default, and needs posters and descriptions to know what belongs together.