Keep the phone's nav under Connections when nothing is running

The chrome stands down for a shell, and it was standing down for the whole
terminal surface. Those parted company when that surface gained a connect page:
with no tabs open it draws a box, a CONNECT button and the machines connected to
before, which is a page in everything but which enum it is in. A third of the
display is worth giving to a shell and is not worth giving to that. Worse, it is
the one screen somebody arrives at by closing their last tab — so the state the
collapsed bar was most likely to be seen in was the state where it left the
system back gesture as the only route to Hosts or Settings.

So RefreshChrome reads one more question. IsTerminalSurface with no tabs joins
the pages in both flags, which keeps the rail and the bar in step: above 600dp
the rail is the bar, and fixing only the narrow layout would leave an unfolded
device on the same screen with the same nothing. The vault header is deliberately
not part of it. The surface draws its own bar with back and the +, and a header
above that is the second row of chrome this head exists to avoid.

The Connections entry lights for the first time, on IsTerminalSurface. It was
left unbound on the argument that the bar was never drawn while that surface was
up, so a lit state was unreachable — that argument is now false, and the flag is
unambiguous on a control that is only drawn in two situations: false on every
page, true on the connect page, and never read while a shell is showing. A bar
sitting under a screen it does not point at is the entry looking broken instead.

Nothing here is testable on this head — the phone's rectangles have no coverage,
for the reasons Phase 8 of manual-checks records — so 11.7 gains the check that
the bar is there with Connections lit, and 11.1 keeps the one that it is gone
with a shell up, which is the half that pays for the arrangement.

src/DodoSSH.Client.Android/Views/TerminalScreen.axaml

@@ -19,9 +19,13 @@
 
     ── the screen a shell gets ───────────────────────────────────────────────────────────────────────────
     A connected phone shows one bar and then the terminal. The vault header, the shells strip and the
-    four-entry bottom bar are all collapsed by PhoneShell while this surface is up, and what replaces them
+    three-entry bottom bar are all collapsed by PhoneShell while a shell is showing, and what replaces them
     is the row below: back, the sessions, and the way to open another one.
 
+    With nothing running it is only the header and the strip. This surface is then the connect page below —
+    a box and the machines connected to before — which is not what the screen was being cleared for, and is
+    the one screen reachable by closing your last tab, so the nav stays. See PhoneShell.RefreshChrome.
+
     That is a trade, and the thing bought is the only one a terminal really wants. At 360dp the chrome this
     screen used to sit inside came to 254 pixels of a roughly 780-pixel display — a third of it — and every
     one of those rows was about somewhere the user was not. What is given up is the bottom bar's one-tap
@@ -389,9 +393,10 @@
       of them.
 
       It lives here rather than in PhoneShell for the reason the add sheet lives in its own screen: nothing
-      but this surface raises it. The scrim reaching only the screen area is not a compromise here the way
-      it was there — the bottom bar is collapsed while a terminal is showing, so the screen area is the
-      display.
+      but this surface raises it. The scrim reaching only the screen area is the full display while a shell
+      is showing, because the bottom bar is collapsed for it. Raised from the connect page it is not, and
+      that lands on the add sheet's own answer: the three destinations under the scrim stay tappable, and for
+      a menu of places to connect from, navigating away is a perfectly good way to decide not to.
 
       Every row navigates away from the terminal. That is not a side effect of the menu, it is the menu:
       each of the three destinations is a picker, and the shell they open lands back on this surface as a