docs(squads): add fa-share-nodes icon to 'Passing data between assistants' nav entry (#1036)

Matches the convention used elsewhere in docs.yml where every page
entry has an icon. fa-share-nodes (connected nodes sharing data)
matches the page's content (three approaches for data flow between
assistants in a squad), is visually distinct from the adjacent
fa-hand-holding-hand on Handoff tool, and does not duplicate
fa-arrow-right-arrow-left already used for Silent handoffs in the
nearby Examples sub-section.

Author: dhruva-reddy

fern/docs.yml

@@ -343,6 +343,7 @@ navigation:
             icon: fa-light fa-hand-holding-hand
           - page: Passing data between assistants
             path: squads/passing-data-between-assistants.mdx
+            icon: fa-light fa-share-nodes
           - section: Examples
             icon: fa-light fa-code
             contents: