Add a Steam Frame build option; no chaperone commit at start; timer-based tick

- CMake option OVRAS_STEAM_FRAME. It is evaluated only in
  src/utils/platform_capabilities.h, which turns it into named capability
  constants and platform defaults.
- Where the chaperone can't be committed (Steam Frame: it shifts the play
  area), MoveCenterTabController no longer commits the working copy at start-up
  or when applying reset data, and doesn't create the init autosave profile.
  Skips are logged once.
- In "vsync disabled" mode the pump timer now runs directly at the custom tick
  rate instead of firing every 1 ms and counting. The Frame defaults to this
  mode at 11 ms (~90 Hz).

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

src/overlaycontroller.cpp

@@ -480,9 +480,7 @@ void OverlayController::SetWidget( QQuickItem* quickItem,
              this,
              SLOT( OnTimeoutPumpEvents() ) );
 
-    // Every 1ms we check if the current frame has advanced (for vsync)
-    m_pumpEventsTimer.setInterval( 1 );
-
+    applyTickInterval();
     m_pumpEventsTimer.start();
 
     m_steamVRTabController.initStage2( this );
@@ -966,6 +964,8 @@ void OverlayController::setVsyncDisabled( bool value, bool notify )
 {
     settings::setSetting( settings::BoolSetting::APPLICATION_vsyncDisabled,
                           value );
+    // The timer interval depends on the mode, see applyTickInterval().
+    applyTickInterval();
     if ( notify )
     {
         emit vsyncDisabledChanged( value );
@@ -1076,6 +1076,8 @@ void OverlayController::setCustomTickRateMs( int value, bool notify )
     settings::setSetting( settings::IntSetting::APPLICATION_customTickRateMs,
                           verifiedTickRate );
     m_verifiedCustomTickRateMs = verifiedTickRate;
+    // In "vsync disabled" mode the timer runs at this interval.
+    applyTickInterval();
 
     if ( notify )
     {
@@ -1083,6 +1085,19 @@ void OverlayController::setCustomTickRateMs( int value, bool notify )
     }
 }
 
+// Sets the interval of m_pumpEventsTimer for the current tick mode:
+// - vsync: every 1 ms, OnTimeoutPumpEvents() checks whether the compositor
+//   started a new frame.
+// - vsync disabled: the timer fires directly at the custom tick rate, so the
+//   process wakes up once per tick instead of every 1 ms.
+// QTimer::setInterval() also restarts a running timer with the new interval.
+void OverlayController::applyTickInterval()
+{
+    m_pumpEventsTimer.setTimerType( Qt::PreciseTimer );
+    m_pumpEventsTimer.setInterval( vsyncDisabled() ? customTickRateMs() : 1 );
+}
+
+// Called by m_pumpEventsTimer, see applyTickInterval().
 // vsync implementation:
 // this function triggers every 1ms
 // this function should remain lightweight and only check if it's time to
@@ -1091,17 +1106,10 @@ void OverlayController::OnTimeoutPumpEvents()
 {
     if ( vsyncDisabled() )
     {
-        // check if it's time for a custom tick rate tick
-        if ( m_customTickRateCounter > customTickRateMs() )
-        {
-            mainEventLoop();
-            m_customTickRateCounter = 0;
-            updateRate.incrementCounter();
-        }
-        else
-        {
-            m_customTickRateCounter++;
-        }
+        // The timer already runs at the custom tick rate: every call is a
+        // tick.
+        mainEventLoop();
+        updateRate.incrementCounter();
     }
 
     // vsync is enabled