Centre a phone row's caption in the row it is given

Button.row sets the height a thumb needs and left the caption's placement to
Avalonia's Stretch default, so the content presenter stretched the caption to
the whole row and a TextBlock draws its line at the top of what it is given —
the same omission the desktop head's ghost/accent/danger rule had.

Most of the thirty-three rows never showed it, which is what made the four that
did look like four unrelated mistakes rather than one rule: a row whose content
is a StackPanel or a Grid of already-centred children is centred whatever this
property says. The four that are a bare TextBlock are FilesScreen's breadcrumb
crumb, its up-one-directory chip and its pinned-path chip, and TerminalScreen's
CLOSE THIS TAB — 36 or 44 tall with no vertical padding, so measured at those
numbers the caption sat flush against the top edge with 21 to 33 pixels of
nothing under it, eleven to seventeen pixels off centre in a control barely
twice that tall.

Nothing is excluded here, unlike the desktop's own sweep: no row's content
depends on being stretched — there is no full-height strip inside any of the
thirty-three, the thing that keeps flat and cat out of the equivalent rule over
there — and the Grids that stop filling hold only children that already centre
themselves, so they land where they always did.

The other two phone classes that do not set it are both fine and neither should
get it. RadioButton.chip declares its own ControlTemplate whose presenter reads
VerticalAlignment="Center" outright, so it centres regardless and the property
would not be read; Button.scrim is the full-screen dimmer behind a sheet and
has no caption at all.

Not covered by a test, and it cannot be from here: there is no Android layout
suite, the desktop harness cannot instantiate net10.0-android views, and
AvaloniaRuntimeXamlLoader — which would let it load Phone.axaml on its own —
lives in a package this repo does not reference. What is verified is that the
head builds, so the Avalonia XAML compiler has accepted the setter, and that
the desktop's own 147 layout tests are unmoved.

src/DodoSSH.Client.Android/Theme/Phone.axaml

@@ -116,11 +116,27 @@
     <Setter Property="FontWeight" Value="SemiBold" />
   </Style>
 
-  <!-- A row in a list: the whole row is the target, and it is 54 tall because a thumb is not a mouse. -->
+  <!--
+    A row in a list: the whole row is the target, and it is 54 tall because a thumb is not a mouse.
+
+    ◆ VerticalContentAlignment, because that height is the whole point of this class and Avalonia's default
+    for content alignment is Stretch — so the content presenter stretched the caption to the full row and a
+    TextBlock draws its line at the TOP of what it is given. Most rows here never showed it, having a
+    StackPanel or a Grid of already-centred children in them, which is what made the four that did look
+    like four unrelated mistakes: the breadcrumb chips and the up-one-directory button on FilesScreen, and
+    TerminalScreen's CLOSE THIS TAB, each a bare TextBlock in a row 36 or 44 tall with no vertical padding.
+    Measured at those numbers, the caption sat flush against the top edge with 21 to 33 pixels below it.
+
+    The desktop head's App.axaml carries the same setter on its own shapes for the same reason, and excludes
+    two of them — see the remark on Button.ghost there. Nothing is excluded here: no row's content depends
+    on being stretched, there being no full-height strip inside any of the thirty-three, and the Grids that
+    stop filling hold only children that already centre themselves, so they land where they always did.
+  -->
   <Style Selector="Button.row">
     <Setter Property="MinHeight" Value="54" />
     <Setter Property="HorizontalAlignment" Value="Stretch" />
     <Setter Property="HorizontalContentAlignment" Value="Stretch" />
+    <Setter Property="VerticalContentAlignment" Value="Center" />
     <Setter Property="Background" Value="Transparent" />
     <Setter Property="BorderThickness" Value="0" />
     <Setter Property="CornerRadius" Value="10" />