v1.3: Auto makeup gain, spectrum analyzer, FIR normalization, README overhaul

- Auto makeup gain: RMS-based loudness compensation from actual FIR response
- Real-time FFT spectrum analyzer behind EQ curves
- FIR normalization fix: flat settings now produce exact 0 dB passthrough
- Brickwall limiter (0 dB ceiling) with toggle
- Drag-and-drop signal chain reordering
- Low FIR tap count warning for 512/1024
- Double-click reset on all knobs
- Comprehensive README with linear phase EQ explanation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.22)
-project(InstaLPEQ VERSION 1.2.2)
+project(InstaLPEQ VERSION 1.3.0)
 
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)