Fix live waveform scaling, drop GTK deps, and document the project

- Tune the live spectrum display to a fixed range matched to real per-FFT-bin
  levels (-40..0 dB) so typical content sits mid-screen instead of flying to
  the top or hugging the bottom; widen the SENS offset control to -48..+24 dB
- Disable JUCE_WEB_BROWSER so the WebKitGTK WebBrowserComponent (unused) is
  compiled out, letting the plugin build on Artix/Arch without GTK/WebKit dev
  headers
- Add a verbose README covering the bands, parameters, controls, structure,
  DSP, build steps, and the Linux/Artix note

CMakeLists.txt

@@ -102,6 +102,12 @@ target_link_libraries(GelykEQ PRIVATE juce::juce_dsp)
 
 target_compile_definitions(GelykEQ PRIVATE JUCE_MODULE_AVAILABLE_juce_dsp=1)
 
+# Gelyk never uses the embedded web browser, so keep JUCE_WEB_BROWSER off.
+# Otherwise juce_gui_extra's WebBrowserComponent pulls in WebKitGTK + GTK dev
+# headers (webkit2gtk, gtk, jsc, libsoup), which would break headless builds
+# like Arch/Artix where those aren't installed.
+target_compile_definitions(GelykEQ PRIVATE JUCE_WEB_BROWSER=0)
+
 target_compile_options(GelykEQ PRIVATE
     $<$<CXX_COMPILER_ID:AppleClang,Clang>:-Wall -Wextra>
 )