vv webcam Unit 1: the vertical (9:16) tier keeps its OWN camera placement per scene

The vertical tier is a centred band crop of the SAME 1920x1080 master (band x
656.25, w 607.5, h 1080), so the 16:9 camera placement (x~1408) falls outside the
cropped window and the creator is simply not in the vertical stream. Each scene
now keeps its own vertical position, size and shape; switching back to 16:9
restores the desktop layout exactly (the creator's locked table, 2026-10-17).

Geometry only - NO render-path change. The preview and the compositor both read
the element's own X/Y/W/H + ClipShape, so the tier switch swaps the LIVE geometry:
- Models/VerticalCameraLayout.cs (new): the pure math - the band, its two 607x540
  areas, the six spots (top/bottom x left/centre/right), the 32px inset and the
  270x152 default tile (480x270 in the 1080x1920 output) in the bottom-right spot,
  the corner the 16:9 default webcam uses.
- Models/WebcamSceneConfig.cs: the vertical placement lives in seven additive
  columns (VerticalX/Y/Width/Height/ClipShape/RectWidth/RectHeight; NULL = "this
  scene has no vertical placement yet"). The 16:9 layout stays in the old columns
  and is parked in the transient Landscape* fields while the vertical tier is
  live; Begin/EndVerticalLayout + CommitLiveLayoutToVertical do the swap. The
  X/Y/W/H overrides clamp every write into the band - outside it the camera is
  invisible in the vertical output.
- Models/SceneElement.cs: X/Y/Width/Height became virtual so the derived element
  constrains every writer (drag, resize handle, typed fields) in ONE choke point
  instead of three writers each re-implementing the rule.
- ViewModels/MainViewModel.Webcam.cs + .Streaming.cs: IsVerticalTier/VerticalBand,
  ResolveVerticalCameraLayout(s) (the tier swap), MoveWebcamInVerticalTier /
  SnapWebcamInVerticalTier (the six-spot snap, by the tile's centre),
  EnsureVerticalCameraLayout; ApplyStreamQuality is the tier-change hook. The
  Live scene gets its small tile automatically on the first vertical switch (the
  vertical stream would otherwise have no camera at all); the other scenes keep
  their 16:9 placement until the creator drags them into the band.
- Controls/PreviewPane.xaml.cs: the drag/resize route through the VM snap under
  the vertical tier instead of free-floating over the master.
  Controls/LeftPanel.xaml: the webcam properties gained a Geometry section
  (X/Y/W/H) for the manual entry the creator asked for, bound to the LIVE
  placement, gated on the VM's IsWebcamSelected (NOT SelectedElement.IsWebcam -
  the TASK 51 test finds that panel by binding text and would match twice).
- The store: seven guarded ADD COLUMNs, the INSERT/SELECT extended, and the
  X/Y/W/H/ClipShape columns stay the 16:9 layout - while the vertical tier is
  live the save writes the parked values there and the live ones into Vertical*.

Test: ytLive.Tests/VerticalWebcamLayoutTests.cs - the ONE Good Dog test. The
vertical tier brings the Live camera INTO the band as a small tile; dragging it to
the top-right lands it top-right inside the band; back to 16:9 the desktop layout
is restored exactly (1408/778/480x270); both placements survive a save + reload.
Full suite 429/429, 0 warnings. LayerReorderPersistenceTests.RealMouseDrag fails
ALONE on a clean tree in this environment - pre-existing flake, proven by stashing
this work, not a regression.

Derivative work: OBS has no built-in per-aspect-ratio layout storage - the
maintainers' answer is "create a second scene and add the scene you want to send
as source" (obsproject.com/forum/threads/161307) - and Streamyard's dual-aspect
guide says the same ("no built-in way to store separate layouts per aspect ratio",
so you rely on manual workarounds and plugins):
https://streamyard.com/blog/dual-aspect-ratio-streaming-tool
Our per-scene, per-tier stored placement, resolved on the tier change, is the
step past both.

Memory in the same commit: ai.md (new section), TASKS.md + TASKS/task-57-*.md
(Unit 1 shipped, Unit 2 = the Chat scene still open), HANDOFF.md, MyMistakes.md
(the per-tier geometry-swap recipe, the binding-text panel trap, the store's
webcam-identity rule) and the Models/Services/ViewModels/Controls index rows.

Controls/LeftPanel.xaml

@@ -252,6 +252,36 @@
                                            Foreground="#a0a0b0" FontSize="10" Margin="0,2,0,0"/>
                             </StackPanel>
 
+                            <!-- Webcam geometry (TASK 57): under the vertical tier the camera
+                                 keeps its OWN placement, so these fields edit the LIVE one —
+                                 the placement the current tier shows. Gated on the VM's
+                                 IsWebcamSelected (the same condition as the mirror/shape row
+                                 above) so the webcam's border/background section stays the
+                                 one panel bound to SelectedElement.IsWebcam. -->
+                            <StackPanel Visibility="{Binding IsWebcamSelected, Converter={StaticResource BoolToVis}}" Margin="0,0,0,8">
+                                <TextBlock Text="Geometry" Foreground="#a0a0b0" FontSize="11" FontWeight="SemiBold" Margin="0,0,0,4"/>
+                                <DockPanel Margin="0,0,0,4">
+                                    <TextBlock DockPanel.Dock="Left" Text="X" Foreground="#a0a0b0" FontSize="11" VerticalAlignment="Center" Width="16"/>
+                                    <TextBox Text="{Binding SelectedElement.X, UpdateSourceTrigger=PropertyChanged, StringFormat=F0}"
+                                             Background="#0f3460" Foreground="#e0d0e0" BorderThickness="1"
+                                             BorderBrush="#2c3a5c" Padding="4,2" FontSize="12"/>
+                                    <TextBlock DockPanel.Dock="Left" Text="  Y" Foreground="#a0a0b0" FontSize="11" VerticalAlignment="Center" Width="20" Margin="8,0,0,0"/>
+                                    <TextBox Text="{Binding SelectedElement.Y, UpdateSourceTrigger=PropertyChanged, StringFormat=F0}"
+                                             Background="#0f3460" Foreground="#e0d0e0" BorderThickness="1"
+                                             BorderBrush="#2c3a5c" Padding="4,2" FontSize="12"/>
+                                </DockPanel>
+                                <DockPanel Margin="0,0,0,4">
+                                    <TextBlock DockPanel.Dock="Left" Text="W" Foreground="#a0a0b0" FontSize="11" VerticalAlignment="Center" Width="16"/>
+                                    <TextBox Text="{Binding SelectedElement.Width, UpdateSourceTrigger=PropertyChanged, StringFormat=F0}"
+                                             Background="#0f3460" Foreground="#e0d0e0" BorderThickness="1"
+                                             BorderBrush="#2c3a5c" Padding="4,2" FontSize="12"/>
+                                    <TextBlock DockPanel.Dock="Left" Text="  H" Foreground="#a0a0b0" FontSize="11" VerticalAlignment="Center" Width="20" Margin="8,0,0,0"/>
+                                    <TextBox Text="{Binding SelectedElement.Height, UpdateSourceTrigger=PropertyChanged, StringFormat=F0}"
+                                             Background="#0f3460" Foreground="#e0d0e0" BorderThickness="1"
+                                             BorderBrush="#2c3a5c" Padding="4,2" FontSize="12"/>
+                                </DockPanel>
+                            </StackPanel>
+
                             <!-- Webcam border config -->
                             <StackPanel Visibility="{Binding SelectedElement.IsWebcam, Converter={StaticResource BoolToVis}}" Margin="0,0,0,8">
                                 <TextBlock Text="Border Color" Foreground="#a0a0b0" FontSize="11" Margin="0,0,0,2"/>