S3+S4: user param auth, static file serving, Docker deploy config

- replace hardcoded benji with ?user= query param
- add GET /api/users and GET /api/me?user= endpoints
- serve frontend static files via tower-http ServeDir
- add multi-stage Dockerfile (Rust + Vite → single image)
- add docker-compose.yml + Caddyfile for apes.unslope.com
- frontend: getCurrentUsername() from URL param → localStorage
- sidebar shows current user

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/colony/src/main.rs

@@ -4,6 +4,7 @@ mod routes;
 use axum::{routing::get, Router};
 use sqlx::sqlite::SqlitePoolOptions;
 use std::env;
+use tower_http::services::{ServeDir, ServeFile};
 
 #[tokio::main]
 async fn main() {
@@ -32,6 +33,8 @@ async fn main() {
 
     let app = Router::new()
         .route("/api/health", get(routes::health))
+        .route("/api/users", get(routes::list_users))
+        .route("/api/me", get(routes::get_me))
         .route(
             "/api/channels",
             get(routes::list_channels).post(routes::create_channel),
@@ -41,6 +44,10 @@ async fn main() {
             "/api/channels/{channel_id}/messages",
             get(routes::list_messages).post(routes::post_message),
         )
+        // Serve frontend static files, fallback to index.html for SPA routing
+        .fallback_service(
+            ServeDir::new("static").fallback(ServeFile::new("static/index.html")),
+        )
         .with_state(pool);
 
     let listener = tokio::net::TcpListener::bind(format!("0.0.0.0:{}", port))