docs: add Plan Mode Default working principle to CLAUDE.md

Author: github-actions[bot]

CLAUDE.md

@@ -157,3 +157,12 @@ This repo uses [Greptile](https://greptile.com) for automated PR reviews. After
 ## Node Version
 
 Requires Node >= 20.
+
+## Working Principles
+
+### 1. Plan Mode Default
+
+* Enter plan mode for ANY non-trivial task (3+ steps or architectural decisions)
+* If something goes sideways, STOP and re-plan immediately – don't keep pushing
+* Use plan mode for verification steps, not just building
+* Write detailed specs upfront to reduce ambiguity