Move backend files to root level for cleaner GitHub display

- Move all backend files from swingmusic/ to root level
- Backend files now display directly on GitHub repository page
- Keep client applications as submodules (swingmusic-android, swingmusic-desktop, swingmusic-webclient)
- Update README to reflect new structure (no cd swingmusic needed)
- Cleaner, more professional GitHub repository layout

Files moved to root:
- src/ (main source code)
- pyproject.toml, requirements.txt, run.py
- swingmusic.spec, uv.lock, version.txt
- services/

Result: GitHub shows backend files directly while maintaining organized structure

src/swingmusic/models/user.py

@@ -0,0 +1,35 @@
+from dataclasses import asdict, field, dataclass
+import json
+
+
+@dataclass(slots=True)
+class User:
+    id: int
+    image: str
+    password: str
+    username: str
+    roles: list[str]
+    extra: dict[str, str] = field(default_factory=dict)
+
+    # NOTE: roles: ['admin', 'user', 'curator']
+    roles: list[str] = field(default_factory=lambda: ["user"])
+
+    def todict(self):
+        this_dict = asdict(self)
+        del this_dict["password"]
+
+        if type(this_dict["roles"]) is str:
+            # INFO: this is an attempt to fix string roles!
+            try:
+                this_dict["roles"] = json.loads(this_dict["roles"])
+            except json.JSONDecodeError:
+                this_dict["roles"] = []
+
+        return this_dict
+
+    def todict_simplified(self):
+        return {
+            "id": self.id,
+            "username": self.username,
+            "firstname": self.extra["firstname"] if self.extra else "",
+        }