Self-heal missing data/links.json instead of crashing

Production 500'd on every request because the ./data volume mount
was an empty host directory, shadowing the seed file baked into the
image. load_data() now creates a minimal default file on first run
if none exists, so an empty/fresh data volume no longer takes the
site down.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app.py

@@ -17,8 +17,23 @@ DATA_FILE = Path(os.environ.get("DATA_FILE", "data/links.json"))
 
 COLORS = ["blue", "green", "orange", "pink"]
 
+DEFAULT_DATA = {
+    "index": {
+        "title": "My Links",
+        "subtitle": "",
+        "subtitle2": "",
+        "footer_label": "",
+        "footer_href": "",
+        "sections": [],
+    }
+}
+
 
 def load_data():
+    if not DATA_FILE.exists():
+        DATA_FILE.parent.mkdir(parents=True, exist_ok=True)
+        save_data(DEFAULT_DATA)
+        return json.loads(json.dumps(DEFAULT_DATA))
     with open(DATA_FILE, "r", encoding="utf-8") as f:
         return json.load(f)