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/domain/tests/canvas.rs

@@ -0,0 +1,125 @@
+use domain::{Canvas, Color, DomainError, Position};
+
+macro_rules! pos {
+    ($x:expr, $y:expr) => {
+        Position::new($x, $y)
+    };
+}
+
+macro_rules! color {
+    ($v:expr) => {
+        Color::new($v)
+    };
+}
+
+macro_rules! assert_pixel {
+    ($canvas:expr, $x:expr, $y:expr, $expected:expr) => {{
+        let (x, y): (u32, u32) = ($x, $y);
+        let idx = y as usize * $canvas.width() as usize + x as usize;
+        let expected = color!($expected);
+        assert_eq!($canvas.pixels()[idx], expected, "pixel at ({x}, {y})");
+    }};
+}
+
+fn small_canvas() -> Canvas {
+    Canvas::new(10, 10)
+}
+
+#[test]
+fn new_canvas_is_all_white() {
+    let canvas = small_canvas();
+    assert_eq!(canvas.pixels().len(), 100);
+    assert!(canvas.pixels().iter().all(|&c| c == Color::white()));
+}
+
+#[test]
+fn dimensions_match_construction() {
+    let canvas = Canvas::new(42, 17);
+    assert_eq!(canvas.width(), 42);
+    assert_eq!(canvas.height(), 17);
+    assert_eq!(canvas.pixels().len(), 42 * 17);
+}
+
+#[test]
+fn place_pixel_updates_correct_position() {
+    let mut canvas = small_canvas();
+    let update = canvas.place_pixel(pos!(3, 4), color!(0xFF0000)).unwrap();
+
+    assert_pixel!(canvas, 3, 4, 0xFF0000);
+    assert_eq!(update.position(), pos!(3, 4));
+    assert_eq!(update.color(), color!(0xFF0000));
+}
+
+#[test]
+fn place_pixel_does_not_affect_neighbors() {
+    let mut canvas = small_canvas();
+    canvas.place_pixel(pos!(5, 5), color!(0xFF)).unwrap();
+
+    for (x, y) in [(4, 5), (6, 5), (5, 4), (5, 6)] {
+        assert_pixel!(canvas, x, y, 0xFFFFFFFF);
+    }
+}
+
+#[test]
+fn place_pixel_overwrites_previous() {
+    let mut canvas = small_canvas();
+    canvas.place_pixel(pos!(0, 0), color!(0xAA)).unwrap();
+    canvas.place_pixel(pos!(0, 0), color!(0xBB)).unwrap();
+    assert_pixel!(canvas, 0, 0, 0xBB);
+}
+
+#[test]
+fn place_pixel_at_boundary() {
+    let mut canvas = small_canvas();
+    assert!(canvas.place_pixel(pos!(9, 9), color!(0xFF)).is_ok());
+    assert!(canvas.place_pixel(pos!(0, 0), color!(0xFF)).is_ok());
+    assert!(canvas.place_pixel(pos!(9, 0), color!(0xFF)).is_ok());
+    assert!(canvas.place_pixel(pos!(0, 9), color!(0xFF)).is_ok());
+}
+
+#[test]
+fn place_pixel_out_of_bounds() {
+    let mut canvas = small_canvas();
+
+    for (x, y) in [(10, 0), (0, 10), (10, 10), (100, 100)] {
+        let result = canvas.place_pixel(pos!(x, y), color!(0xFF));
+        assert!(
+            matches!(result, Err(DomainError::PixelOutOfBounds(_))),
+            "({x}, {y}) should be out of bounds"
+        );
+    }
+}
+
+#[test]
+fn from_pixels_with_correct_size() {
+    let pixels = vec![color!(0xAA); 25];
+    let canvas = Canvas::from_pixels(5, 5, pixels).unwrap();
+    assert_eq!(canvas.width(), 5);
+    assert_eq!(canvas.height(), 5);
+    assert!(canvas.pixels().iter().all(|&c| c == color!(0xAA)));
+}
+
+#[test]
+fn from_pixels_with_wrong_size() {
+    let too_few = vec![color!(0); 10];
+    let too_many = vec![color!(0); 30];
+
+    for pixels in [too_few, too_many] {
+        assert!(
+            matches!(
+                Canvas::from_pixels(5, 5, pixels),
+                Err(DomainError::InvalidCanvasData { .. })
+            ),
+            "should reject pixel vec that doesn't match dimensions"
+        );
+    }
+}
+
+#[test]
+fn from_pixels_preserves_content() {
+    let mut pixels = vec![Color::white(); 9];
+    pixels[4] = color!(0xFF0000); // center pixel of 3x3
+    let canvas = Canvas::from_pixels(3, 3, pixels).unwrap();
+    assert_pixel!(canvas, 1, 1, 0xFF0000);
+    assert_pixel!(canvas, 0, 0, 0xFFFFFFFF);
+}