Add vitepress docs

docs/net/sync.md

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+# Sync
+
+The Sync utilities in `@welshman/net` provide methods for synchronizing events between relays and repositories, primarily using NIP-77 (Negentropy) when available, with fallback to traditional sync methods.
+
+## Overview
+
+```typescript
+import {sync, pull, push} from '@welshman/net'
+
+// Three main operations:
+// 1. pull: Get events from relays
+// 2. push: Send events to relays
+// 3. sync: Bidirectional sync
+```
+
+These utilities are primarily used by:
+- `Repository` for syncing with relays
+- `FeedController` for initial feed loading
+
+## Basic Usage
+
+```typescript
+import {sync, pull, getFilterSelections} from '@welshman/net'
+
+// Sync user profile data
+const syncProfiles = async (pubkeys: string[]) => {
+  await sync({
+    // What to sync
+    filters: [{
+      kinds: [0],
+      authors: pubkeys
+    }],
+
+    // Which relays
+    relays: ctx.app.router
+      .ForPubkeys(pubkeys)
+      .getUrls(),
+
+    // Local events to consider
+    events: repository.query([{
+      kinds: [0],
+      authors: pubkeys
+    }])
+  })
+}
+
+// Initial feed load with negentropy
+const loadFeed = async () => {
+  await pull({
+    filters: [{
+      kinds: [1],
+      limit: 100
+    }],
+    relays: ctx.app.router
+      .ForUser()
+      .getUrls(),
+    events: [], // No local events yet
+    onEvent: (event) => {
+      // Handle new events
+    }
+  })
+}
+```
+
+Sync operations:
+- Use NIP-77 when supported by relay
+- Fall back to traditional sync
+- Handle bidirectional sync
+- Support filtered sync
+- Track sync progress