docs: unify the call chain on Build (Hands==Build per ORGANISM.md)

The boundary line read '-> Hands (execute)' while ORGANISM.md and the generated
organism map say 'Build'. Part of the organism docs sweep (#84, WS1).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ERDgNVKpQohYXVcJwAHzmw

Author: claude

AGENTS.md

@@ -8,7 +8,7 @@ release?" gate.
 
 ## The boundary
 
-The organs, boundaries and the `Brain → Heart (gate) → Hands (execute)` call
+The organs, boundaries and the `Brain → Heart (gate) → Build (execute)` call
 chain are defined once in `PyAutoBrain/ORGANISM.md`. Heart's side of it:
 **observer only** — it reads and emits the authoritative
 green/stale/yellow/red verdict, never writes into other repos, and never