App commands and --ha-remove (iteration 2, step 6)

The platform accepts app commands (D43): flags that get a
QCoreApplication like the manifest commands and run prepare() and then
the new hook runCommand(). The app's --ha-remove clears the device's
retained topics, so HA deletes the device; uninstall.sh runs it after
stopping the app and before unregistering from SteamVR.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -112,19 +112,21 @@ into Qt events.
 - `src/app/DashboardApplication` is the **base class of every app** (in `vrdashboard_core`):
   CLI, logging, SteamVR connection, backend selection, surfaces, controller navigation, and the
   modes (overlay, `--desktop`, `--desktop-novr`, `--snapshot`, `--benchmark`, manifest
-  install).
+  install, app commands).
   - **Inheritance for the app, components for the surfaces** (the user's decision, after
     trying composition): the app derives from `DashboardApplication`. In its constructor it
     configures (`addSurface`, optional `setAppKey`/`setDisplayName`) and passes its own
-    command-line options (`QCommandLineOption` list) to the base constructor. It overrides
-    the hooks `prepare(QString*)` (first; mode and app key known, no engine/surfaces/SteamVR
-    yet; returning false ends `exec()` with exit code 1), `loading()` (backends + shared
-    engine exist, QML not loaded) and `started()` (everything runs). In the hooks, protected
+    command-line options and its commands (two `QCommandLineOption` lists, D38, D43) to the
+    base constructor. It overrides the hooks `prepare(QString*)` (first; mode and app key
+    known, no engine/surfaces/SteamVR yet; returning false ends `exec()` with exit code 1),
+    `loading()` (backends + shared engine exist, QML not loaded), `started()` (everything
+    runs) and `runCommand(name)` (mode `Command`, after `prepare()`, nothing else exists). In the hooks, protected
     accessors give the running state: `mode()`, `appKey()`, `appName()`, `isOptionSet()`,
     `optionValue()`, `engine()`, `surfaces()`, `surface()` (primary), `surface(id)`,
     `vrRuntime()`, `navigation()`. The app is `src/Dashboard.h/.cpp`.
-  - The base constructor creates the `QGuiApplication` (`QCoreApplication` for manifest
-    commands), so derived members can be QObjects with timers.
+  - The base constructor creates the `QGuiApplication` (`QCoreApplication` for manifest and
+    app commands: decided from the raw `argv` before parsing), so derived members can be
+    QObjects with timers.
   - All QML and surfaces are torn down **at the end of `exec()`**, while the derived object
     and its members (e.g. QML singletons) still exist.
 - `src/app/Surface` is **one view**: its QML root (from the app's module), renderer, render