docs: add Effector definition node in diagram and bold caption

Made-with: Cursor

Author: Jah-yee

profile/README.md

@@ -25,9 +25,10 @@ graph LR
 
   Brain["Brain / LLMs"]:::brain --> Body["Body / Runtimes"]:::body
   Body --> Hands["Hands / Effectors"]:::hands
+  Hands --> EffNode["Effector = the smallest capability unit an agent can discover, inspect, run, compose, and carry across runtimes."]:::hands
 ```
 
-*Effector = the smallest capability unit an agent can discover, inspect, run, compose, and carry across runtimes.*
+**Effector** = the smallest capability unit an agent can discover, inspect, run, compose, and carry across runtimes.
 
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