v1.0.0 — Hexagonal architecture rewrite

Restructure the monolithic 252-line main.rs into a 10-crate workspace
with clean hexagonal architecture, swappable adapters, and a production-
ready deployment pipeline.

Backend architecture:
- domain: Canvas, Color/Position/PixelUpdate value objects, port traits
  (CanvasStore, CanvasPersistence, EventBroadcaster), BroadcastEvent
- application: use cases (place_pixel, get_state, save/restore snapshot,
  connect/disconnect), AppState with Arc snapshot cache
- config: AppConfig structs + ConfigSource trait
- api-types: shared DTOs, event name constants
- adapters: config-env, canvas-file, http-axum (rust-embed), socketio,
  websocket — all behind port traits, swappable via feature flags
- server: composition root with graceful shutdown (SIGTERM/SIGINT)

Frontend:
- Transport abstraction: Socket.IO and native WebSocket via VITE_TRANSPORT
- Canvas zoom/pan with mouse wheel, pinch-to-zoom, and +/- buttons
- ImageData rendering (~50x faster than fillRect loop)
- Touch support, responsive CSS scaling, mobile-friendly layout
- OG/Twitter Card meta tags for rich link previews

Production:
- Docker: musl static build on scratch — 2.73MB image
- CI workflows for Gitea and GitHub Actions (fmt, clippy, test, Docker push)
- deploy.sh for private registry
- 39 unit tests across domain and application
- Zero unwraps, zero unsafe, graceful error handling with tracing
- Periodic canvas snapshots with rotation, restored on startup
- All config via environment variables with typed defaults

crates/application/tests/soldiers.rs

@@ -0,0 +1,96 @@
+mod common;
+
+use domain::BroadcastEvent;
+
+#[test]
+fn connect_increments_count() {
+    let (state, _) = common::test_state();
+    assert_eq!(
+        application::soldiers::connect::execute(&state, "a".into()),
+        1
+    );
+    assert_eq!(
+        application::soldiers::connect::execute(&state, "b".into()),
+        2
+    );
+    assert_eq!(
+        application::soldiers::connect::execute(&state, "c".into()),
+        3
+    );
+}
+
+#[test]
+fn disconnect_decrements_count() {
+    let (state, _) = common::test_state();
+    application::soldiers::connect::execute(&state, "a".into());
+    application::soldiers::connect::execute(&state, "b".into());
+
+    assert_eq!(application::soldiers::disconnect::execute(&state, "a"), 1);
+    assert_eq!(application::soldiers::disconnect::execute(&state, "b"), 0);
+}
+
+#[test]
+fn disconnect_unknown_user_is_harmless() {
+    let (state, _) = common::test_state();
+    application::soldiers::connect::execute(&state, "a".into());
+    assert_eq!(
+        application::soldiers::disconnect::execute(&state, "unknown"),
+        1
+    );
+}
+
+#[test]
+fn connect_publishes_soldier_count() {
+    let (state, spy) = common::test_state();
+    application::soldiers::connect::execute(&state, "a".into());
+
+    let events = spy.events();
+    assert_eq!(events.len(), 1);
+    assert!(matches!(events[0], BroadcastEvent::SoldierCountChanged(1)));
+}
+
+#[test]
+fn disconnect_publishes_soldier_count() {
+    let (state, spy) = common::test_state();
+    application::soldiers::connect::execute(&state, "a".into());
+    application::soldiers::disconnect::execute(&state, "a");
+
+    let events = spy.events();
+    assert_eq!(events.len(), 2);
+    assert!(matches!(events[1], BroadcastEvent::SoldierCountChanged(0)));
+}
+
+#[test]
+fn disconnect_clears_cooldown() {
+    let (state, _) = common::test_state();
+    application::soldiers::connect::execute(&state, "user-1".into());
+
+    application::canvas::place_pixel::execute(
+        &state,
+        application::canvas::place_pixel::Command {
+            user_id: "user-1",
+            position: domain::Position::new(0, 0),
+            color: domain::Color::new(0xFF),
+        },
+    )
+    .unwrap();
+
+    application::soldiers::disconnect::execute(&state, "user-1");
+
+    // Reconnect with same ID — cooldown should be gone
+    application::soldiers::connect::execute(&state, "user-1".into());
+    let result = application::canvas::place_pixel::execute(
+        &state,
+        application::canvas::place_pixel::Command {
+            user_id: "user-1",
+            position: domain::Position::new(1, 1),
+            color: domain::Color::new(0xAA),
+        },
+    )
+    .unwrap();
+
+    assert!(matches!(
+        result,
+        application::canvas::place_pixel::Outcome::Placed(_)
+    ));
+}