test(avalonia): headless tests for rendering, change events, overlays and theme

feat: bottom-nav, edge-menu and blocks

In an app with an <App>.Application project (clean architecture), a bare
`Application` inside <App>.App.Components.UI resolves to that namespace and
the app fails to build with CS0234. The MAUI shell and the Avalonia shell and
toast now write Microsoft.Maui.Controls.Application / Avalonia.Application.
A template test keeps bare `Application` out of every template.

The focus glow was added on focus and cleared on blur. Adding or removing a
Shadow on Android makes MAUI re-wrap the Border's native view (removeView +
add), which detaches the focused EditText: focus jumps to the first focusable
view, the keyboard closes and typing goes nowhere. The shadow is now always
set and only its opacity changes (0 idle, 0.35 focused or in error).

With ShellTheme.SyncSystemBars, backing out of the app at the root and
reopening it creates a new activity whose bars were never themed (black, page
no longer edge to edge), so apps needed `window.Created += ShellTheme.Apply()`.
The shell now applies the bars again whenever a page appears.

Android wraps an InputTransparent (or shadowed / clipped) view in a
WrapperView after its handler has applied the view's translation, scale and
rotation to the view itself. Later changes move only the wrapper, so the inner
view keeps the first values for good:

- theme-toggle: the moon stayed at half size and turned after switching to
  dark (its hidden state when the handler was created);
- bottom-nav: the Default indicator sat about 25 dp right of the active item
  after the handler was re-created with the page kept (a new activity), and
  stayed offset on every later switch.

ShellPlatform.KeepTransformsOnWrapper (Android only) resets the inner view
when the handler connects and re-applies the transforms to the wrapper. Icon
uses it, which also covers chevrons and spinners, and so do bottom-nav's
indicator, glyph, circle and icon host.

fix: Android findings from ShellLedger (Application name, input focus, system bars, wrapped transforms)

The overlay layer wraps a page's content in a Grid. It was set up on
PageAppearing, which on a Shell route switch runs after the page's views
have loaded, so they got Unloaded and Loaded again, and a view that
cancels its work on Unloaded lost its first load.

The layer is now set up on Application.DescendantAdded, as the page joins
the app and before its views load. PageAppearing stays as the fallback
for a page whose content is set later.

Checked on Windows: a GoToAsync("//route") switch gave the page's views
Loaded 2 / Unloaded 1 before and 1 / 0 after; push, window page swap and
start-up were already fine.

Four common dashboard icons from ShellIcons (Lucide 0.475.0), for MAUI and Avalonia; 114 icons in the template now.

… and input

For MAUI and Avalonia, with demo sections on both:

- data-table: DataTableColumn.Cell draws any view in a cell (a badge, a
  link); filter and sort still use Property / Value
- button: ButtonSize.Inline (h-auto p-0) for a link in a line of text or
  at a card's edge
- sheet: SheetHeader, SheetTitle, SheetDescription and SheetFooter, new
  CLI targets installed with sheet
- card: CardHeader.Action at the top right (shadcn's CardAction), and
  views inside the header sit on the title's line and wrap under it
- stat-card: ValueTone (Default, Success, Warning, Destructive), a value
  row that wraps so the pill drops under a long value, IsLoading
  (skeletons; stat-card now depends on skeleton) and Size Sm
- input, input-group: Variant="Password" masks the text and adds an eye
  button that shows it (keeps focus, named for screen readers);
  IsPassword still masks without the button. InputVariant lives in
  Input, so input-group now depends on input

Headless tests for each, and registry tests for the new targets and
dependencies.

…states and password inputs

Also documents theme tokens on spans and runs, and when the page layer wraps a page's content.

feat: slots and states for data table, button, sheet, card, stat card and input