Fix YAML boolean parsing: quote ticker "ON" (ON Semiconductor)

YAML treats bare `ON` as boolean True, causing TypeError in re.match()
when yfinance tries to use it as a symbol string.

https://claude.ai/code/session_01LbgD64GPmP5tS7j4uavkCa

Author: claude

config.yaml

@@ -34,7 +34,7 @@ universe:
     - APH
     - FTNT
     - NXPI
-    - ON
+    - "ON"
     - MPWR
     - KEYS
     - TEL