Rename Sync docs to Edge Cookie External Sync (#788)

Update the guide page title, sidebar label, and intro language to "Edge Cookie External Sync". Reword the opening paragraph and modify phrasing with data sharing agreement language. Page URL is unchanged so existing links keep resolving.

Co-authored-by: Jason Evans <jevans@jevans-m5-mbp-16.local>

Author: jevansnyc

docs/.vitepress/config.mts

@@ -118,7 +118,10 @@ export default withMermaid(
               text: 'Proxy Signing',
               link: '/guide/proxy-signing',
             },
-            { text: 'Collective Sync', link: '/guide/collective-sync' },
+            {
+              text: 'Edge Cookie External Sync',
+              link: '/guide/collective-sync',
+            },
           ],
         },
         {

docs/guide/collective-sync.md

@@ -1,6 +1,6 @@
-# Collective Sync Architecture
+# Edge Cookie External Sync Architecture
 
-Trusted Server supports cross-publisher data sharing through a **Collective Sync** model. Publishers who share the same EC secret key can synchronize user data across their properties, enabling privacy-preserving audience insights without third-party cookies.
+Trusted Server supports ID syncing. Publishers who have engaged in an agreement with identity partners can use our sync endpoints found below.
 
 ## Overview
 
@@ -31,11 +31,11 @@ sequenceDiagram
 
 ## Architecture Principles
 
-| Component        | Role            | Characteristics                                        |
-| ---------------- | --------------- | ------------------------------------------------------ |
-| **KV Store**     | Hot cache       | Fast reads (~1ms), edge-local, eventually consistent   |
-| **Object Store** | Source of truth | Durable, supports range queries, sync endpoint         |
-| **Secret Key**   | Shared salt     | Distributed out-of-band, enables collective membership |
+| Component        | Role            | Characteristics                                           |
+| ---------------- | --------------- | --------------------------------------------------------- |
+| **KV Store**     | Hot cache       | Fast reads (~1ms), edge-local, eventually consistent      |
+| **Object Store** | Source of truth | Durable, supports range queries, sync endpoint            |
+| **Secret Key**   | Shared salt     | Distributed out-of-band, enables a data sharing agreement |
 
 ## Configuration
 
@@ -105,7 +105,7 @@ The Object Store maintains a richer record with full history:
 
 ### Initial Sync
 
-When a new publisher joins the collective, they perform a full sync:
+When a new publisher has a new agreement, they perform a full sync:
 
 ```http
 GET /sync?type=full