android: the toolbar moves to the top, and the note says when it saved

The capture sheet's drag handle cost a strip of screen and did nothing a back
gesture does not already do. The toolbar takes that strip instead, which is
where it belonged once one surface served both writing and editing: the
keyboard owns the bottom of the display for most of a note's life, so a bar
down there spends its time riding on the IME.

The bottom is now the answer to "did that land". There is no save button —
writes are continuous, so a button offering to do what already happened would
be a lie with a tap attached — but that left nothing on screen saying the work
was safe. Not saved yet → Saving… → Edited just now is the whole lifecycle in
the corner, and someone who watches it once never has to be told that closing
a note keeps it. DateUtils formats the relative part, so plurals and
"yesterday" are not this app's problem to solve twice.

Shape: the screen keeps the sheet's rounded top and its gap below the status
bar, so opening a note still reads as something rising over the board. Full
height rather than a real ModalBottomSheet — a sheet spends a writing session
negotiating with the IME for the bottom half of the display, and the
swipe-down it buys is a gesture back already does.

Both content colours on the card are spelled out. Surface and Scaffold each
default theirs to contentColorFor(their container), which returns Unspecified
for anything that is not a colour-scheme role; a note tint never is. That is
the same default that made the last toolbar invisible in dark mode, latent in
two more places.

Also: the running LinearProgressIndicator is gone, since the corner line now
says the same thing without moving the text; and the SaveText comment in
BoardViewModel still claimed saves happened on close.

android/app/src/main/res/values/strings.xml

@@ -41,6 +41,10 @@
     <string name="editor_remove_label">Remove label</string>
     <string name="editor_reminder">Set a reminder</string>
     <string name="editor_more">More actions</string>
+    <string name="editor_saving">Saving…</string>
+    <string name="editor_unsaved">Not saved yet</string>
+    <string name="editor_edited">Edited %1$s</string>
+    <string name="editor_just_now">just now</string>
     <string name="editor_pin">Pin</string>
     <string name="editor_unpin">Unpin</string>
     <string name="editor_labels">Labels…</string>