feat: automated stable releases, versioned ISOs, and Hub version badge

- Add release-stable.sh script with automatic tagging, CHANGELOG updates,
  GitHub/Gitea release creation, and VERSION file management
- Update iso/common.nix to include version from VERSION file in ISO filename
- Add VERSION file (current: 1.0.3)
- Polish OS version badge in Sovran Hub header (top-right)
- Update README.md download link to versioned ISO
- Update CHANGELOG.md with existing tags (v1.0.0 – v1.0.3)

Co-authored-by: arena-agent <297053741+arena-agent@users.noreply.github.com>

app/sovran_systemsos_web/server.py

@@ -2274,13 +2274,30 @@ async def api_logout(request: Request):
     return response
 
 
+def _get_sovran_version() -> str:
+    """Read the OS version from the VERSION file."""
+    try:
+        with open("/etc/nixos/VERSION", "r") as f:
+            return f.read().strip()
+    except FileNotFoundError:
+        try:
+            with open("VERSION", "r") as f:  # fallback for development
+                return f.read().strip()
+        except FileNotFoundError:
+            return "dev"
+    except Exception:
+        return "dev"
+
+
 @app.get("/", response_class=HTMLResponse)
 async def index(request: Request):
+    sovran_version = _get_sovran_version()
     return templates.TemplateResponse(
         request=request,
         name="index.html",
         context={
             "asset_version": ASSET_VERSION,
+            "sovran_version": sovran_version,
         },
     )