P1-R3: Initial project infrastructure

- Project directory structure: docs/, src/, build/, recipes/, scripts/, wiki/
- README.md with project overview and status
- .editorconfig for consistent code style
- .gitignore for Python, C/C++, kernel, and build artifacts
- docs/research/: system research report + base OS decision
- docs/audio-stack-config.md: audio stack configuration notes
- config/: JACK, ALSA, CPU performance configs
- Preserved research from P1-R1 and P1-R2 tasks

.gitignore

@@ -0,0 +1,60 @@
+# Raspberry Pi RT Audio Mixer — .gitignore
+
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+*.egg-info/
+dist/
+/build/*
+!/build/.gitkeep
+*.egg
+.eggs/
+venv/
+.venv/
+env/
+
+# C/C++
+*.o
+*.obj
+*.a
+*.la
+*.lo
+*.dll
+*.dylib
+*.exe
+*.out
+*.app
+
+# Kernel build artifacts
+*.ko
+*.mod.c
+*.mod
+modules.order
+Module.symvers
+.tmp_versions/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.DS_Store
+Thumbs.db
+
+# Environment
+.env
+.env.local
+*.log
+
+# Cross-compilation
+toolchains/
+sysroot/
+
+# Package files
+*.deb
+*.rpm
+*.tar.gz
+*.tar.xz