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

pubspec.yaml

@@ -0,0 +1,21 @@
+name: chat_server
+description: A self-hosted chat server with home server identity model.
+version: 0.1.0
+
+environment:
+  sdk: '>=3.0.0 <4.0.0'
+
+dependencies:
+  relic: ^1.0.0
+  objectbox: ^4.0.0
+  dart_jsonwebtoken: ^2.14.0
+  bcrypt: ^1.1.3
+  crypton: ^2.2.1
+  crypto: ^3.0.3
+  collection: ^1.18.0
+  hotreloader: ^1.0.6
+
+dev_dependencies:
+  objectbox_generator: ^4.0.0
+  build_runner: ^2.4.0
+  lints: ^4.0.0