feat(swarm): Add federated followers and following endpoints

- Create new swarm endpoints for fetching user followers list at /api/swarm/users/[handle]/followers
- Create new swarm endpoints for fetching user following list at /api/swarm/users/[handle]/following
- Add SwarmFollowerUser and SwarmFollowingUser interfaces for federated user data
- Implement local and remote follower/following aggregation in swarm endpoints
- Update local followers endpoint to fetch data from remote swarm nodes
- Update local following endpoint to fetch data from remote swarm nodes
- Add error handling and database availability checks for all endpoints
- Include node domain and timestamp metadata in swarm responses
- Support pagination with configurable limit parameter (max 100)
- Enable cross-node follower/following visibility for federated social graph

src/app/api/users/[handle]/followers/route.ts

@@ -4,6 +4,24 @@ import { eq } from 'drizzle-orm';
 
 type RouteContext = { params: Promise<{ handle: string }> };
 
+/**
+ * Fetch followers list from a remote swarm node
+ */
+const fetchSwarmFollowers = async (handle: string, domain: string, limit: number) => {
+    try {
+        const protocol = domain.includes('localhost') ? 'http' : 'https';
+        const url = `${protocol}://${domain}/api/swarm/users/${handle}/followers?limit=${limit}`;
+        const res = await fetch(url, {
+            headers: { 'Accept': 'application/json' },
+            signal: AbortSignal.timeout(5000),
+        });
+        if (!res.ok) return null;
+        return await res.json();
+    } catch {
+        return null;
+    }
+};
+
 export async function GET(request: Request, context: RouteContext) {
     try {
         const { handle } = await context.params;
@@ -11,6 +29,29 @@ export async function GET(request: Request, context: RouteContext) {
         const { searchParams } = new URL(request.url);
         const limit = Math.min(parseInt(searchParams.get('limit') || '20'), 50);
 
+        // Check if this is a remote user
+        const [remoteHandle, remoteDomain] = cleanHandle.split('@');
+        
+        if (remoteDomain) {
+            // Fetch from remote swarm node
+            const swarmData = await fetchSwarmFollowers(remoteHandle, remoteDomain, limit);
+            if (swarmData?.followers) {
+                // Transform to include full handles for local users on that node
+                const followers = swarmData.followers.map((f: any) => ({
+                    id: f.isRemote ? f.handle : `${f.handle}@${remoteDomain}`,
+                    handle: f.isRemote ? f.handle : `${f.handle}@${remoteDomain}`,
+                    displayName: f.displayName,
+                    avatarUrl: f.avatarUrl,
+                    bio: f.bio,
+                    isRemote: true,
+                    isBot: f.isBot,
+                }));
+                return NextResponse.json({ followers, nextCursor: null });
+            }
+            // If swarm fetch fails, return empty
+            return NextResponse.json({ followers: [], nextCursor: null });
+        }
+
         // Return empty if no database
         if (!db) {
             return NextResponse.json({ followers: [], nextCursor: null });