feat(settings): position slide-out notifications

App Settings now chooses one of six ToastArea positions (left/right ×
top/center/bottom), defaulting to the existing bottom-right. The setting is
persisted per profile and the toast area moves immediately; edge gutters keep
bottom notifications above the footer.

ToastPositionIntegrationTests covers live repositioning and restart persistence.
617 tests green, clean build with 0 warnings.

Reference scan: OBS Notifier supports user-configured notification placement:
https://github.com/DmitriySalnikov/OBSNotifier

ViewModels/index.md

@@ -20,6 +20,7 @@ areas' docs in their own rows keeps this index small to read.
 | `MainViewModel.Socials.cs` | Social bar (global resource, overlaid on every scene): `_socials`/`_socialBarFrame`/`_socialValidator` (`ISocialValidator`/`HttpSocialValidator`), `HasSocials`/`SocialBarVisible`/`SocialBarDotBrush`/`SocialBarGlowBrush`/`Socials`/`SocialBarTop`, `OpenSocialDialogCommand`/`OpenSocialDialog` (spawns `SocialsDialogViewModel` + window; saved copy replaces `_socials`), `NotifySocialsChanged`/`RenderSocialBarFrame` (`SocialBarRenderer` → immutable `_socialBarFrame` the frame pump reads), fediverse heal `HealFediverseSoftwareAsync` (static, test-facing) + `HealFediverseSoftwareInBackground`, bar edge toggle `SetSocialBarPosition`/`ToggleSocialBarPosition`. `BarOnBrush`/`BarOffBrush`/`CreateBrush` stay in core (shared tokens). |
 | `MainViewModel.Streaming.cs` | Go-live/record + health + quality tiers + session UI. **Stream state:** `StreamStatus`/`StreamVisibility` setters + `_streamStatus` field, `IsOffline`/`IsLive`/`IsLivePrivate`. **Go-live flow:** `StartSession` (routes by pill state) → `BeginRecordOnly` (signed-out local recording) or `BeginGoLive` (GoLive dialog → captures title/description/visibility + `BroadcastForm.CaptureGoLive` → `PrepareAndStartLiveAsync`: reusable stream → `CreateBroadcast` (stores `_currentBroadcastId`) → empty-metadata warn → chat poll start (liveChatId) → `_framePump.StartAsync()` + health poll; failures → `StreamStatus.Error`, never a crash); `StartRecordFile` (auto-named `ty-…-0000.mp4`) + `FinalizeRecordingAsync` (rename modal, `UniquePath`); `StopStream` (posts Offline, stops chat/audio pipe/pump, clears `_currentBroadcastId`; session/token deliberately NOT cleared — sign-out stays explicit). **Health:** `CurrentHealth`/`ResetHealth`/`ApplyHealth`/`OnFramePumpHealthUpdated` (marshal `FramePump.HealthUpdated` off the stderr thread), `PollHealthAsync`/`OnHealthPollTick`/`ApplyHealthIssue` (report-by-exception banner `HealthIssueBanner`/`HealthIssueBackground` via `StreamHealthReporter`). **Session timer:** `_liveTimer` (ctor-wired) `UpdateSessionTimer`/`OnLiveTimerTick`/`LiveElapsedText`/`_recDotPulse`. **Start/End UI:** mode switch `RecordPillOn`/`OnAirPillOn`, top-bar worlds (`ShowIdleWorld`/`ShowRecordAction`/`ShowStreamActions`/`ShowSignInButton`/`ShowAvatarButton`, reality line `RunningVisible`/`RunningText`/`RunningDotBrush`, Test gate `ShowTestButton`/`CanStartTest` — `RaiseTopBarModes()`), `ShowPrimaryStartButton`/`CanStartSession`/`ShowEndStreamButton`/`EndButtonText`, REC sign `RecDotBrush`/`RecTextBrush`/`RecDotOpacity`/`OnAirBrush`, live window tokens `WindowTitle`/`TopBarBackground`/`PreviewGlow*` via `UpdateLiveVisuals`; `ChooseRecordFolder`/`ResetRecordFolder`/`_recordFolder`/`RecordFolderDisplay`/`DefaultRecordFolder`. **Resolution dropdown:** `QualityOptions`/`SelectedQuality`/`ResolutionHelp`/`ApplyStreamQuality` + `OutputRect*`/`DimRects`/`IsOutputCropped`/`ResolutionBadgeText` over the 1920×1080 master; **TASK 57:** the tier change also resolves every scene's camera placement (the vertical tier brings the vertical placements in, 16:9 restores the desktop layout — see `MainViewModel.Webcam.cs`). **Pipeline bits:** `_framePump`/`_liveTimer`/`_healthPollTimer` fields, `BuildEncoderOptions`. Commands `StartStreamCommand`/`EndStreamCommand`/`ChooseRecordFolderCommand`/`ResetRecordFolderCommand`. Broadcast pull-out: `CurrentBroadcastId`/`BroadcastForm`. **TASK 57 (Unit 2):** the tier change also raises `CanToggleClipShape` (the circle option disappears in the vertical Chat layout). |
 | `MainViewModel.Overlays.cs` | Settings/bug/feature/about panels + creator-hub links: panel state `IsSettingsOpen`/`IsBugOpen`/`IsFeatureOpen`/`IsAboutOpen` (via `SetPanel` → `IsAnyOverlayOpen`), `IsLicensesOpen` (flips `IsHubVisible`), `OverlayTitle`, `ShowOverlay` (one-panel exclusivity), `ShowAbout` (returns to the About hub) + `ShowLicenses` (loads shipped `THIRD-PARTY-NOTICES.txt` into `LicensesText` in-app); bug/feature report `BugReportText`/`BugReportEmail`/`FeatureRequestText`/`FeatureRequestEmail` + `SubmitBug`/`SubmitFeature`/`ComposeEmail`/`OpenUrl`; About hub consts `ChannelUrl`/`MastodonUrl`/`CoffeeUrl` + `PremiumUrl` (`https://llamacasty.com`, opens only when explicitly clicked) + `IsPremiumAvailable` + `SupportEmail` + `AppVersionLabel`; commands `OpenSettingsCommand`/`OpenBugCommand`/`OpenFeatureCommand`/`OpenAboutCommand`/`CloseOverlayCommand`/`SubmitBugCommand`/`SubmitFeatureCommand`/`OpenChannelCommand`/`OpenMastodonCommand`/`OpenCoffeeCommand`/`OpenPremiumCommand`/`OpenLicensesCommand`. A locked quality selection opens About without changing the tier. Ctor command assignments stay in core. |
+| `MainViewModel.Settings.cs` | App Settings drawer state + global slide-out toast position (`ToastPosition`), persisted in `LayoutStore.Settings`; `ToastAreaMargin` keeps the six supported positions aligned to the window edges/safe footer gap. |
 | `MainViewModel.Chat.cs` | Chat overlay + preview pipeline: `ChatMessages` (500-message cap; clear-on-fade), `OnChatMessageReceived` (marshal `_youtubeChat.MessageReceived` onto the dispatcher, switch previews mock→real, then feed **both** component layers), fade `_chatFadeTimer`/`ResetChatFadeTimer` (shortest `ChatFadeSeconds` across chat layers); live render `RenderChatBox` (called from `ResolveOutputFrame`, stays in core) + preview render `UpdateChatBoxPreview` (bitmap onto `chatBox.VideoImageSource`); mock preview `MockChatMessages`/`StartMockChatPreview`/`StopMockChatPreview`/`RunMockChatPreviewAsync`/`_mockChatCts`; `UpdateActiveChatBoxPreviews` (wires Chat* property-change subscriptions + first render); `CanAddYouTubeChat` (one-per-layout gate), `ShowChatInactiveMessage` (`!IsLive`). **Alerts (TASK 43):** same facade for the native alert box — `_alertLayer` (`AlertOverlayLayer`), `RenderAlertBox`/`UpdateAlertBoxPreview`, `UpdateActiveAlertBoxPreviews`, `CanAddAlerts` (one alert zone per layout). Ctor wiring (`MessageReceived` hookup, `new ChatBoxRenderer()`, `new AlertRenderer()`, `LoadLayout` preview start, `_youtubeChat.Dispose` + `_alertLayer.Dispose`) stays in core. |
 | `MainViewModel.Logs.cs` | Non-edit left-panel tab state and bounded current-launch log collections; refreshes the process-local AppLog snapshot while Logs is selected, pins Class 1 before Class 2 until acknowledged, then returns entries to the LIFO timeline; stops its dispatcher timer on shutdown. |
 | `GoLiveViewModel.cs` | Start Stream dialog: **account row** (saved channel shown with Change Account, or Sign in to YouTube; Start gated on `IsSignedIn`/`IsBusy`) + title/description + **locked Visibility (always "Private" — ship step 7, no dropdown)**, start/cancel requests |