Reorganize repository structure for better organization

- Move backend code to swingmusic/ folder
- Move client applications to root level (swingmusic-android, swingmusic-desktop, swingmusic-webclient)
- Remove intermediate backend/ and clients/ folders
- Update README with new folder structure and setup instructions
- Clean and organized repository layout

swingmusic/requirements.txt

@@ -0,0 +1,28 @@
+pillow>=11.1.0
+Flask>=3.1.0
+Flask-Cors>=3.0.10
+requests>=2.27.1
+colorgram.py>=1.2.0
+tqdm>=4.65.0
+tinytag>=2.1.1
+Unidecode>=1.3.6
+psutil>=5.9.4
+show-in-file-manager>=1.1.4
+flask-compress>=1.13
+tabulate>=0.9.0
+setproctitle>=1.3.2
+locust>=2.20.1
+watchdog>=4.0.0
+flask-jwt-extended>=4.6.0
+sqlalchemy>=2.0.31
+memory-profiler>=0.61.0
+sortedcontainers>=2.4.0
+xxhash>=3.4.1
+ffmpeg-python>=0.2.0
+schedule>=1.2.2
+flask-openapi3==3.0.2
+rapidfuzz==3.11.0
+pendulum>=3.0.0
+pystray>=0.19.5
+waitress==3.0.2; sys_platform == 'win32'
+bjoern>=3.2.2; sys_platform != 'win32'