feat: add presets, Randomize button, menu highlight, finer LFO depth, preset-switch fade-out

- PresetManager: add ~40 new presets including a new Techno category with
  LFO-to-OSC-pitch movement, plus Bass/Lead/Pad/Keys/Brass/Strings/Wind/
  Arp/Pluck/FX expansions
- UI: add RANDOM button; highlight the currently selected entry in all
  dropdown menus (incl. ticking the active preset in the preset browser)
- LFO depth: finer 0.001 step with a skew curve so the lower range resolves
  much finer than the upper range (shared by LFO1 and LFO2)
- DSP: fade out active voices over 250ms on preset change / randomize so long
  release tails from the previous sound are silenced
- Update bg.png

Source/PluginEditor.cpp

@@ -118,7 +118,7 @@ void ComboBoxLookAndFeel::drawComboBox(juce::Graphics& g, int width, int height,
 
 void ComboBoxLookAndFeel::drawPopupMenuItem(juce::Graphics& g, const juce::Rectangle<int>& area,
                                             bool isSeparator, bool /*isActive*/,
-                                            bool isHighlighted, bool /*isTicked*/,
+                                            bool isHighlighted, bool isTicked,
                                             bool /*hasSubMenu*/, const juce::String& text,
                                             const juce::String& /*shortcutKeyText*/,
                                             const juce::Drawable* /*icon*/,
@@ -130,12 +130,19 @@ void ComboBoxLookAndFeel::drawPopupMenuItem(juce::Graphics& g, const juce::Recta
         return;
     }
 
+    // Persistent highlight for the currently selected (ticked) entry
+    if (isTicked && !isHighlighted) {
+        g.setColour(juce::Colour(0xffccaa44).withAlpha(0.3f));
+        g.fillRoundedRectangle(area.reduced(2).toFloat(), 3.0f);
+    }
+
     if (isHighlighted) {
         g.setColour(juce::Colour(0xffccaa44));
         g.fillRoundedRectangle(area.reduced(2).toFloat(), 3.0f);
     }
 
-    g.setColour(isHighlighted ? juce::Colour(0xff1a1a1a) : juce::Colour(0xffcccccc));
+    g.setColour(isHighlighted ? juce::Colour(0xff1a1a1a)
+                              : (isTicked ? juce::Colour(0xffccaa44) : juce::Colour(0xffcccccc)));
     g.setFont(juce::Font(13.0f));
     g.drawText(text, area.reduced(8, 0), juce::Justification::centredLeft, true);
 }
@@ -537,6 +544,12 @@ MainContentComponent::MainContentComponent(ChromaFlockProcessor& p)
         applyCurrentPreset();
     };
 
+    randomizeButton.setColour(juce::TextButton::buttonColourId, juce::Colour(0xff2a2a2a));
+    randomizeButton.setColour(juce::TextButton::textColourOffId, juce::Colour(0xffccaa44));
+    randomizeButton.setLookAndFeel(&comboLaf);
+    randomizeButton.onClick = [this]() { randomizeParameters(); };
+    addAndMakeVisible(randomizeButton);
+
     auto& presets = processorRef.presetManager.getPresets();
     if (!presets.empty()) {
         currentPresetIndex = 0;
@@ -645,12 +658,19 @@ void MainContentComponent::showPresetMenu() {
     std::vector<juce::String> menuOrder;
 
     auto categories = processorRef.presetManager.getCategories();
+
+    juce::String currentName;
+    auto& allPresets = processorRef.presetManager.getPresets();
+    if (currentPresetIndex >= 0 && currentPresetIndex < static_cast<int>(allPresets.size()))
+        currentName = allPresets[currentPresetIndex].name;
+
     for (auto& cat : categories) {
         juce::PopupMenu subMenu;
         auto presets = processorRef.presetManager.getPresetsInCategory(cat);
         for (auto& preset : presets) {
             menuOrder.push_back(preset.name);
-            subMenu.addItem(static_cast<int>(menuOrder.size()), preset.name);
+            bool isCurrent = (preset.name == currentName);
+            subMenu.addItem(static_cast<int>(menuOrder.size()), preset.name, true, isCurrent);
         }
         menu.addSubMenu(cat, subMenu);
     }
@@ -675,6 +695,7 @@ void MainContentComponent::applyCurrentPreset() {
     auto& presets = processorRef.presetManager.getPresets();
     if (presets.empty()) return;
     currentPresetIndex = juce::jlimit(0, static_cast<int>(presets.size()) - 1, currentPresetIndex);
+    processorRef.fadeOutActiveVoices(0.25f);
     processorRef.presetManager.applyPreset(presets[currentPresetIndex].name, processorRef.apvts);
     patchLCD.setText(presets[currentPresetIndex].name);
 
@@ -685,6 +706,30 @@ void MainContentComponent::applyCurrentPreset() {
     setupSyncKnob(delayTimeKnob, delayTimeAttach, delayBeatAttach, "delayTime", "delayBeat", delaySyncBox);
 }
 
+void MainContentComponent::randomizeParameters() {
+    juce::Random rand;
+    processorRef.fadeOutActiveVoices(0.25f);
+    for (auto* p : processorRef.getParameters()) {
+        auto* rap = dynamic_cast<juce::RangedAudioParameter*>(p);
+        if (rap == nullptr)
+            continue;
+        const auto& id = rap->paramID;
+        if (id == "octaveTranspose" || id == "semitoneTranspose")
+            continue;
+        float v = rand.nextFloat();
+        if (id == "masterLevel")
+            v = 0.4f + 0.6f * v;
+        rap->setValueNotifyingHost(v);
+    }
+
+    patchLCD.setText("RANDOM");
+
+    // Re-sync the rate/beat knob attachments to match the randomized sync states.
+    setupSyncKnob(lfo1RateKnob, lfo1RateAttach, lfo1BeatAttach, "lfo1Rate", "lfo1Beat", lfo1SyncBox);
+    setupSyncKnob(lfo2RateKnob, lfo2RateAttach, lfo2BeatAttach, "lfo2Rate", "lfo2Beat", lfo2SyncBox);
+    setupSyncKnob(delayTimeKnob, delayTimeAttach, delayBeatAttach, "delayTime", "delayBeat", delaySyncBox);
+}
+
 void MainContentComponent::paint(juce::Graphics& g) {
     g.fillAll(juce::Colour(0xff1a1a1a));
 
@@ -915,6 +960,7 @@ void MainContentComponent::resized() {
 
     // --- PRESET + SCALE ---
     presetButton.setBounds(20, 8, 90, 28);
+    randomizeButton.setBounds(20, 42, 90, 28);
     patchLCD.setBounds(118, 8, 360, 28);
     prevPresetButton.setBounds(486, 8, 28, 28);
     nextPresetButton.setBounds(518, 8, 28, 28);