Add bidirectional OSC scaling for TouchOSC slider synchronization

[Copilot]

TouchOSC requires 0.5x scaling on outbound messages. Without compensating on inbound messages, sliders desynchronize when controlled from TouchOSC.

Changes

Outbound scaling (all float values)

• Added OSC_SCALE_FACTOR = 0.5f in OSCManager.h
• Applied in OSCManager::sendMessage() for all float/double values
• Integer and string values pass through unchanged

Inbound scaling (selective controls only)

• Added OSC_INVERSE_SCALE_FACTOR = 2.0f in OSCManager.h
• Applied to incoming values in control registrations:
  • /OutGainSlider - main output gain
  • /DrySlider - dry/wet mix
  • /Peer{1-16}Level - peer level/gain
  • /Peer{1-16}Pan - peer pan

Unchanged controls

• All other peer controls (compressor, expander, EQ, reverb send)
• All main controls (mute, metronome, recording, options)
• All InputGroup controls

Example

// Outbound: Application → TouchOSC
processor.getOSCManager().sendMessage("/OutGainSlider", 1.0);
// TouchOSC receives: 0.5

// Inbound: TouchOSC → Application  
oscManager.registerControl("/OutGainSlider", [this](const OSCMessage& msg) {
    float value = msg[0].getFloat32() * OSC_INVERSE_SCALE_FACTOR;  // 0.5 * 2.0 = 1.0
    mOutGainSlider->setValue(value);
});

This maintains bidirectional synchronization: App(1.0) --[×0.5]--> TouchOSC(0.5) --[×2.0]--> App(1.0)

Original prompt

In the branch add-juce-osc, we need to add a global constant to centrally manage a scaling factor for outbound OSC messages. Specifically, implement a constexpr float scaleFactor = 0.5f in the appropriate source files under Source to ensure all OSC messages sent use this scale factor. The intention is to minimize duplication and ensure future flexibility while maintaining compatibility with TouchOSC or similar controls that expect normalized ranges. Update related OSC send calls to incorporate this scaling factor using existing message send logic.

This pull request was created from Copilot chat.

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[mendeni]

I've confirmed the correct values are being sent and received between our application and TouchOSC.