Detect HW acceleration; default lava off on software renderer; release probe WebGL context

Probes UNMASKED_RENDERER_WEBGL once per page via a throwaway WebGL context; defaults the lava subsystem off on a positive software-renderer match or total WebGL failure; releases the throwaway context via WEBGL_lose_context after reading the renderer string to avoid exhausting the browser's per-page context limit.

DeepDrftPublic.Client/Services/WaveformVisualizerControlState.cs

@@ -160,6 +160,47 @@ public sealed class WaveformVisualizerControlState
     /// </summary>
     public event Action? Changed;
 
+    // Whether the one-time, capability-driven default has been applied this session. The default-set
+    // (lava off when the browser has no WebGL hardware acceleration) must run exactly once — on the
+    // first interactive render, before the listener has touched a toggle — so it sets the *initial
+    // default* and never clobbers a later explicit in-session toggle. Scoped with the rest of this
+    // state, so it survives SPA navigation (a remounted visualizer does not re-apply) and resets on a
+    // fresh page load (F5 re-probes).
+    private bool _capabilityDefaultApplied;
+
+    /// <summary>
+    /// Applies the hardware-capability default exactly once per session: when the browser reports no
+    /// WebGL hardware acceleration, the lava subsystem (the expensive, main-thread software-rendered
+    /// part that starves audio decode) defaults <c>off</c> while the waveform stays <c>on</c>. With
+    /// acceleration present this is a no-op — lava keeps its <see cref="DefaultLavaEnabled"/> on-state.
+    ///
+    /// <para>
+    /// Idempotent and guarded: only the FIRST call this session has any effect, so it sets the initial
+    /// default and never overrides a listener's explicit toggle (the control remains fully functional —
+    /// a user on a software renderer may re-enable lava at their own risk). Mutates, coerces
+    /// Theater Mode, then raises <see cref="Changed"/> once so the controls UI, the visualizer bridge,
+    /// and the Theater observers all reflect the default in a single cycle. Called by the visualizer
+    /// bridge on first interactive render, once JS interop (the probe) is available.
+    /// </para>
+    /// </summary>
+    /// <param name="hardwareAccelerated">
+    /// The probe result — <c>true</c> when WebGL hardware acceleration is present (or the renderer is
+    /// unknown/masked, favoring the common case), <c>false</c> only on a positive software-renderer
+    /// match or total WebGL failure.
+    /// </param>
+    public void ApplyCapabilityDefault(bool hardwareAccelerated)
+    {
+        if (_capabilityDefaultApplied) return;
+        _capabilityDefaultApplied = true;
+
+        // Accelerated (or unknown): keep the as-shipped defaults — no observer churn.
+        if (hardwareAccelerated) return;
+
+        LavaEnabled = false; // the expensive subsystem off; WaveformEnabled stays at its default (true).
+        CoerceTheaterMode();
+        NotifyChanged();
+    }
+
     /// <summary>
     /// Enforces the Theater-Mode invariant: Theater Mode cannot remain on when both visualizer
     /// subsystems are off (there is nothing to go to theater FOR). Call this after mutating