feat(stream): retry a dropped push instead of ending the session (TASK 32·1)

A dead encoder used to run the whole stop path, so a one-second blip ended the broadcast. Now a dropped
push is relaunched against the same ingest while the broadcast is still alive.

- `Services/StreamRetryPolicy.cs` — immediate, +1 s, +2 s, +3 s. Minimum waits on purpose (creator
  ruling): YouTube's grace is short, so every second not pushing is grace spent.
- `Services/StreamRecovery.cs` — the loop, with the audio pipe recreated before every attempt (its
  server is single-instance and unusable after the old client dies, so a naive relaunch fails on a
  missing input). After a push comes up it asks the API whether the broadcast survived: "complete"
  ends recovery as `BroadcastComplete` instead of showing a live sign over a dead stream; an API
  hiccup counts as recovered rather than ending a healthy session.
- `FramePump.EncoderFailed` — a dead push is recoverable; a compositor fault still goes through
  `Failed` and ends the session, because retrying it would loop.
- `MainViewModel.Recovery.cs` — wires the steps, reports each episode into the left panel alert stack
  (one row per episode, updated in place, log range painted), and cancels on Stop.
- Alert stack polish: a rule and a gap now separate the stack from the scene layers (they read as one
  list before), and the licence indicator uses the creator's wording — `STEAM ID NOT PRESENT` /
  `Steam ID Limit: 30fps` / `Click for More Info`, becoming `STEAM ID PRESENT` / `60fps` with a close
  control once owned.

Tests: `StreamRecoveryTests` (schedule, recover on attempt 2 with the pipe restarted each time,
complete-broadcast honesty, unknown liveness, give-up, cancel, audio-restart fault),
`FramePumpTests` now pin that process death raises `EncoderFailed` and not `Failed`.
FAST gate: 538 passed (one documented pre-existing audio failure), 0 warnings.

Controls/LeftPanel.xaml

@@ -49,8 +49,11 @@
                          ownership is verified (that close is permanent). Clicking a row runs its
                          action: the licence indicator opens About, an event opens the Logs tab with
                          that event's lines painted. -->
-                    <ItemsControl Grid.Row="0" ItemsSource="{Binding AttentionAlerts}" Margin="0,0,0,6"
-                                  Visibility="{Binding HasAttentionAlerts, Converter={StaticResource BoolToVis}}">
+                    <!-- Alerts and the panel content are different kinds of thing (state vs. the
+                         scene you are editing), so they are separated by space AND a rule: without it
+                         the stack read as the first rows of the layer list (creator, 2026-11-05). -->
+                    <StackPanel Grid.Row="0" Visibility="{Binding HasAttentionAlerts, Converter={StaticResource BoolToVis}}">
+                    <ItemsControl ItemsSource="{Binding AttentionAlerts}" Margin="0,0,0,2">
                         <ItemsControl.ItemTemplate>
                             <DataTemplate>
                                 <Border Margin="0,0,0,4" Padding="8,6" CornerRadius="4" Cursor="Hand"
@@ -89,6 +92,8 @@
                             </DataTemplate>
                         </ItemsControl.ItemTemplate>
                     </ItemsControl>
+                        <Border Style="{StaticResource PropertyDivider}" Margin="0,4,0,10"/>
+                    </StackPanel>
 
                     <!-- Edit mode (offline): layers + properties -->
                     <Grid Grid.Row="1" Visibility="{Binding IsEditMode, Converter={StaticResource BoolToVis}}">