fix: point watch token guidance at token file

[robinbraemer]

Summary

• fix WatchService endpoint-token mismatch guidance to reference the actual token sources: token.json or CONNECT_TOKEN
• update the focused formatter test to prevent config.yml guidance from returning

Verification

• ./gradlew :core:test --tests com.minekube.connect.watch.WatchAuthFailureMessageTest --no-daemon
• ./gradlew build --no-daemon

Follow-up for #44 (comment)