t-354.1: Enhance dev.md with init/recovery phases

Enhance dev.md workflow with init check and failure recovery phases.

Add: 1. Phase 0: Init (Pre-flight)

• Verify git status is clean
• If namespace provided, verify it builds
• STOP if either fails

2. On Failure section

• Revert changes with git checkout -- .
• Report what went wrong

This makes dev.md equivalent to Coder.hs functionality.