feat: Initial MVP with home server identity model

- User model with Ed25519 keypair identity
- Register/login on home server (creates keypair)
- Join guest servers with signature verification
- Public endpoints for cross-server identity
- Channel and message CRUD
- JWT authentication middleware

Architecture: Home server model, no federation, client-driven sync

lib/src/handlers/channel_handlers.dart

@@ -0,0 +1,82 @@
+import 'package:chat_server/models.dart';
+import 'package:chat_server/objectbox.g.dart';
+import 'package:relic/relic.dart';
+
+import '../utils/extensions.dart';
+
+/// Get all channels
+Future<Response> getChannelsHandler(Request req) async {
+  final channels = channelBox.getAll();
+
+  return Response.ok(
+    body: {
+      'channels': channels
+          .map((c) => {
+                'id': c.id,
+                'name': c.name,
+                'description': c.description,
+                'createdAt': c.createdAt.toIso8601String(),
+              })
+          .toList(),
+    }.toBody,
+  );
+}
+
+/// Create a channel (requires 'admin' role)
+Future<Response> createChannelHandler(Request req) async {
+  final body = await req.asJson();
+  final name = (body['name'] as String?)?.trim().toLowerCase().replaceAll(' ', '-');
+  final description = body['description'] as String?;
+
+  if (name == null || name.isEmpty) {
+    return Response.badRequest(
+      body: Body.fromString('Channel name required'),
+    );
+  }
+
+  // Check if channel exists
+  final existing = channelBox.query(Channel_.name.equals(name)).build().findFirst();
+  if (existing != null) {
+    return Response.badRequest(
+      body: Body.fromString('Channel already exists'),
+    );
+  }
+
+  final channel = Channel(name: name, description: description);
+  final id = channelBox.put(channel);
+
+  return Response.ok(
+    body: {
+      'id': id,
+      'name': name,
+      'description': description,
+      'createdAt': channel.createdAt.toIso8601String(),
+    }.toBody,
+  );
+}
+
+/// Get channel by ID
+Future<Response> getChannelHandler(Request req, String channelIdStr) async {
+  final channelId = int.tryParse(channelIdStr);
+  if (channelId == null) {
+    return Response.badRequest(
+      body: Body.fromString('Invalid channel ID'),
+    );
+  }
+
+  final channel = channelBox.get(channelId);
+  if (channel == null) {
+    return Response.notFound(
+      body: Body.fromString('Channel not found'),
+    );
+  }
+
+  return Response.ok(
+    body: {
+      'id': channel.id,
+      'name': channel.name,
+      'description': channel.description,
+      'createdAt': channel.createdAt.toIso8601String(),
+    }.toBody,
+  );
+}