docs(squads): restore main's docs.yml and re-add 'Passing data' nav entry

The original commit 7c1bb11 inadvertently bundled three reverts of
unrelated upstream changes alongside the squads-page nav entry.
Investigation showed the entire fern/docs.yml file in that commit
predated three independent main commits — pattern-consistent with
a stale local copy of the file having been committed wholesale,
rather than a targeted nav addition.

This commit restores fern/docs.yml to origin/main verbatim and then
adds ONLY the new 'Passing data between assistants' nav entry under
the Squads section, immediately after 'Handoff tool'.

Specifically restored from main:

- Changelog tab display-name 'What's New?' / slug 'whats-new' (set
  by #1021 'Rename Changelog to What's New?')
- 'Email address reading' nav entry under Assistants (set by #1024)
- 'Monitoring' section + Quickstart entry under Observability (set
  by #991)

Net effect on PR #1033's docs.yml diff: only the 2-line addition of
the new Squads nav entry remains. Verified via:

  git diff origin/main -- fern/docs.yml

shows exactly the +2 lines for the new page entry, nothing else.

Author: dhruva-vapi

fern/docs.yml

@@ -76,8 +76,8 @@ tabs:
     icon: fa-light fa-square-terminal
     slug: cli
   changelog:
-    display-name: Changelog
-    slug: changelog
+    display-name: What's New?
+    slug: whats-new
     changelog: ./changelog
     icon: history
   mcp:
@@ -156,6 +156,8 @@ navigation:
                 path: assistants/background-speech-denoising.mdx
               - page: Pronunciation dictionaries
                 path: assistants/pronunciation-dictionaries.mdx
+              - page: Email address reading
+                path: assistants/email-address-reading.mdx
           - section: Model configurations
             icon: fa-light fa-waveform-lines
             contents:
@@ -321,6 +323,12 @@ navigation:
               - page: Quickstart
                 path: observability/scorecard-quickstart.mdx
                 icon: fa-light fa-rocket
+          - section: Monitoring
+            icon: fa-light fa-bell
+            contents:
+              - page: Quickstart
+                path: observability/monitoring-quickstart.mdx
+                icon: fa-light fa-rocket
 
       - section: Squads
         contents:
@@ -335,7 +343,6 @@ navigation:
             icon: fa-light fa-hand-holding-hand
           - page: Passing data between assistants
             path: squads/passing-data-between-assistants.mdx
-            icon: fa-light fa-arrow-right-arrow-left
           - section: Examples
             icon: fa-light fa-code
             contents:
@@ -861,7 +868,9 @@ redirects:
   - source: /developer-documentation
     destination: /introduction
   - source: /documentation/general/changelog
-    destination: /changelog
+    destination: /whats-new
+  - source: /changelog
+    destination: /whats-new
   - source: /api-reference/assistants/create-assistant
     destination: /api-reference/assistants/create
   - source: /api-reference/assistants/get-assistant