chore: track data/demo.db and update gitignore

.gitignore

@@ -35,9 +35,11 @@ dist/
 .wheels/
 
 # --- Data & databases ---
-data/
+data/*
 *.sqlite
 *.db
+# allow demo database for the public demo
+!data/demo.db
 
 # --- Logs & temp files ---
 logs/

app/routers/nl2sql.py

@@ -122,7 +122,10 @@ router = APIRouter(prefix="/nl2sql")
 # -------------------------------
 DB_MODE = os.getenv("DB_MODE", "sqlite").lower()  # "sqlite" or "postgres"
 POSTGRES_DSN = os.getenv("POSTGRES_DSN")
-DEFAULT_SQLITE_PATH: str = os.getenv("DEFAULT_SQLITE_DB", "data/Chinook_Sqlite.sqlite")
+# Default demo DB used when no db_id is provided (can be full Chinook or a tiny demo DB)
+DEFAULT_SQLITE_PATH: str = os.getenv(
+    "DEFAULT_SQLITE_PATH", "data/Chinook_Sqlite.sqlite"
+)
 
 # Runtime upload storage
 _DB_UPLOAD_DIR = os.getenv("DB_UPLOAD_DIR", "/tmp/nl2sql_dbs")
@@ -308,10 +311,9 @@ async def upload_db(file: UploadFile = File(...)):
 def _final_schema_preview(db_id: Optional[str], provided_preview: Optional[str]) -> str:
     if provided_preview and provided_preview.strip():
         return provided_preview
-    if db_id:
-        adapter = _select_adapter(db_id)
-        return _derive_schema_preview(adapter) or ""
-    return ""
+
+    adapter = _select_adapter(db_id)  # works for both None and explicit db_id
+    return _derive_schema_preview(adapter) or ""
 
 
 @router.get("/health")

temp.py

@@ -0,0 +1,34 @@
+import sqlite3
+
+path = "data/demo.db"
+conn = sqlite3.connect(path)
+cur = conn.cursor()
+
+print(f"Inspecting: {path}\n")
+
+# --- tables
+cur.execute("SELECT name FROM sqlite_master WHERE type='table';")
+tables = [t[0] for t in cur.fetchall()]
+
+print("=== TABLES ===")
+for t in tables:
+    print("-", t)
+
+# --- schema
+print("\n=== SCHEMA ===")
+for table in tables:
+    print(f"\n--- {table} ---")
+    cur.execute(f"PRAGMA table_info('{table}');")
+    for col in cur.fetchall():
+        print(col)
+
+# --- sample rows
+print("\n=== SAMPLE ROWS (LIMIT 5) ===")
+for table in tables:
+    print(f"\n--- {table} ---")
+    cur.execute(f"SELECT * FROM {table} LIMIT 5;")
+    rows = cur.fetchall()
+    for r in rows:
+        print(r)
+
+conn.close()