Add delay and reverb FX section with full DSP

Rename the DIST section to FX and expand it with tempo-synced delay
(Time/Strength/Sync) and Schroeder reverb (Roomsize/Strength/Diffusion).
New FxProcessor runs post-voice on the stereo bus; widen the editor to
1280px to fit the new section. Add a TestHost check that the FX tail
rings out after note release.

tests/TestHost.cpp

@@ -299,6 +299,84 @@ static int testProcessorRendering()
 
     std::cout << "Master=0 silences output OK\n";
 
+    // delay + reverb FX: after the note releases, the FX tail must ring out
+    // (delay repeats / reverb decay) instead of going silent, with no NaN/blow-up.
+    *processor.getAPVTS().getRawParameterValue ("master")   = 1.0f;
+    *processor.getAPVTS().getRawParameterValue ("release")  = 0.01f;
+    *processor.getAPVTS().getRawParameterValue ("delayStrength")   = 0.0f;
+    *processor.getAPVTS().getRawParameterValue ("reverbStrength")  = 0.0f;
+
+    const int releaseBlock = numBlocks / 2;
+
+    const auto renderFxTail = [&] () -> double
+    {
+        processor.reset();
+        processor.prepareToPlay (44100.0, 512);
+
+        juce::AudioBuffer<float> fxBlock (2, blockSize);
+        juce::MidiBuffer fxMidi;
+        double tailSum = 0.0;
+        int tailSamples = 0;
+        bool finite = true;
+
+        for (int b = 0; b < numBlocks; ++b)
+        {
+            fxBlock.clear();
+            fxMidi.clear();
+
+            if (b == 0)
+                fxMidi.addEvent (juce::MidiMessage::noteOn (1, 60, 0.9f), 0);
+            else if (b == releaseBlock)
+                fxMidi.addEvent (juce::MidiMessage::noteOff (1, 60), 0);
+
+            processor.processBlock (fxBlock, fxMidi);
+
+            if (b > releaseBlock)
+                for (int c = 0; c < 2; ++c)
+                    for (int i = 0; i < blockSize; ++i)
+                    {
+                        const float s = fxBlock.getSample (c, i);
+                        if (! std::isfinite (s))
+                            finite = false;
+                        tailSum += (double) s * s;
+                        ++tailSamples;
+                    }
+        }
+
+        if (! finite)
+            return -1.0;
+
+        return std::sqrt (tailSum / (double) std::max (1, tailSamples));
+    };
+
+    const double dryTail = renderFxTail();
+
+    if (dryTail > 1e-3)
+    {
+        std::cout << "FAILED: dry tail after release should be silent, got " << dryTail << "\n";
+        return 1;
+    }
+
+    *processor.getAPVTS().getRawParameterValue ("delayStrength") = 0.8f;
+    *processor.getAPVTS().getRawParameterValue ("delayTime")     = 0.4f;
+    *processor.getAPVTS().getRawParameterValue ("delaySync")     = 1.0f;
+    *processor.getAPVTS().getRawParameterValue ("reverbStrength") = 0.8f;
+    *processor.getAPVTS().getRawParameterValue ("reverbRoom")     = 0.9f;
+    *processor.getAPVTS().getRawParameterValue ("reverbDiffusion") = 1.0f;
+
+    const double wetTail = renderFxTail();
+
+    if (wetTail < 0.0)
+        return 1;
+
+    if (wetTail < 1e-3)
+    {
+        std::cout << "FAILED: delay/reverb tail is inaudible (wet=" << wetTail << ")\n";
+        return 1;
+    }
+
+    std::cout << "Delay + reverb FX OK (dryTail=" << dryTail << " wetTail=" << wetTail << ")\n";
+
     return 0;
 }