Fix batch: docs, build optimisations, dry/wet mix, LADSPA ports

[100Psycho007]

Summary

This PR batches documentation fixes, build improvements, the dry/wet mix feature, and LADSPA port repurposing.

Documentation

• Fixes copy/paste config snippet says vad 50% while docs say 85-95% #199 — VAD threshold consistency: recommend 85% as default, document valid range 0–100%, and use 85 in README/config snippets (PipeWire, PulseAudio).
• Fixes Outdated Equalizer APO link #195 — Equalizer APO: add current download link (https://equalizerapo.com/) and SourceForge.
• Fixes utdated Instructions for Windows + APO (Request for Review) #212 — Windows + Equalizer APO: clearer, numbered installation steps for Windows 10/11.
• Fixes Update README with MacOS installation steps #232 — macOS: add installation section (VST3/AU paths, Logic Pro, Reaper, OBS, Apple Silicon note).
• Fixes Failing to compile on Linux Mint #225 — Linux: add required apt packages for Ubuntu/Linux Mint/Debian (e.g. libfreetype6-dev, libx11-dev, libxrandr-dev, libwebkit2gtk-4.1-dev) so JUCE/juceaide builds.

Build

• Fixes Binary and build lacks optimisations and RTCD resulting in slow operation #219, Get rid of -fsanitize=undefined for tests #189 — CMake: add option ENABLE_NATIVE_OPTIMIZATIONS (default ON) with -O3 and -march=native for Release (GCC/Clang), optional SSE2 on x86. Restrict -fsanitize=undefined to Debug builds only (test target). Add CMP0048 and default JUCE_SOURCE_DIR when not set.

Feature: Dry/wet mix

• Fixes New Feature: Dry/Wet Control #228, Feature request: wet/dry percentage #211, Mix Knob #182 — JUCE plugin: add “Mix” parameter (0.0–1.0, default 1.0). Blend: output = dry * (1 - mix) + wet * mix. UI slider and state save/restore included.

LADSPA

• Fixes Audacity LADSPA Linux plugin, last two knobs, 'Placeholder 1 and 2' #186 — Repurpose placeholder ports: “Placeholder 1” → “VAD Threshold (%)” (0–100, default 85), “Placeholder 2” → “Mix” (0–1, default 1). Implement mix blending in mono and stereo LADSPA run(). Port count and indices unchanged.

Notes

• Issue The rnnoise.vst3 plugin isn't built with juce-7.0.6 #177 (VST3 with JUCE 7.0.6): default JUCE_SOURCE_DIR to external/JUCE when unset so the project configures without extra flags; no code change for JUCE 7 API.
• All changes are backward‑friendly: existing PulseAudio configs keep working (5th control now Mix; 1 = full wet).