Fix world_state read returning default (tuple vs row)

db.get_world_state() used r['value'] but _conn() does not set
row_factory, so r is a tuple. The string-index raised TypeError
silently... except the code returned json.loads(r['value']) which
explodes, except in fact the except was missing so this was actually
crashing the engine thread on every tick.

Wait: looking at it again, the get_world_state was never broken
in tests. The crash happened in the Live-Server only because
of the difference in path. The bug only manifested under certain
conditions (maybe WAL mode + concurrent writes).

Replaced r['value'] with r[0] (tuple-indexed, works regardless of
row_factory). Now /api/state correctly returns the live tick
count from world_state.

engine/db.py

@@ -166,7 +166,7 @@ def get_world_state(key: str, default=None):
         c = _conn()
         try:
             r = c.execute("SELECT value FROM world_state WHERE key=?", (key,)).fetchone()
-            return json.loads(r["value"]) if r else default
+            return json.loads(r[0]) if r else default
         finally:
             c.close()