design: three tokens the sweep needed — positive, scrim-dark, scrim-dark-strong

The palette had no green for status and no black scrim, so two surfaces were about to either
invent literals or misuse an accent. Creator's call (2026-10-30): give green a token rather
than painting "connected" blue, which already means five other things.

- `positive` #22c55e — STATUS ONLY (connected, applied, healthy). Never an accent, never a
  button fill; the doc says so and the guard parses the doc.
- `scrim-dark` #26000000 (15% black) and `scrim-dark-strong` #00000080 (50%) — the preview's dim
  strips and heavy overlays. 18 sites justify a token, and they are structural, not decoration.
- LeftPanel's ✓ confirm now wears `positive` instead of the interactive accent, matching the
  status rule the new token states.

DesignTokensTests still green: the doc is the contract, so the three new rows demanded three
new brushes and got them.

Themes/Tokens.xaml

@@ -23,6 +23,8 @@
     <SolidColorBrush x:Key="Brush.OutlineVariant" Color="#1e293b"/>
     <SolidColorBrush x:Key="Brush.ScrimSoft" Color="#22FFFFFF"/>
     <SolidColorBrush x:Key="Brush.ScrimStrong" Color="#26FFFFFF"/>
+    <SolidColorBrush x:Key="Brush.ScrimDark" Color="#26000000"/>
+    <SolidColorBrush x:Key="Brush.ScrimDarkStrong" Color="#00000080"/>
 
     <!-- Text -->
     <SolidColorBrush x:Key="Brush.OnSurface" Color="#dae2fd"/>
@@ -37,6 +39,7 @@
     <SolidColorBrush x:Key="Brush.Secondary" Color="#ffb95f"/>
     <SolidColorBrush x:Key="Brush.SecondaryContainer" Color="#ee9800"/>
     <SolidColorBrush x:Key="Brush.Attention" Color="#ff8c3a"/>
+    <SolidColorBrush x:Key="Brush.Positive" Color="#22c55e"/>
     <SolidColorBrush x:Key="Brush.Error" Color="#ef4444"/>
     <SolidColorBrush x:Key="Brush.ErrorContainer" Color="#93000a"/>
     <SolidColorBrush x:Key="Brush.OnError" Color="#ffdad6"/>