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/config/src/lib.rs

@@ -0,0 +1,61 @@
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum ConfigError {
+    #[error("invalid value for '{field}': {reason}")]
+    InvalidValue { field: String, reason: String },
+
+    #[error("failed to load config: {0}")]
+    LoadFailed(String),
+}
+
+#[derive(Debug, Clone)]
+pub struct AppConfig {
+    pub server: ServerConfig,
+    pub canvas: CanvasConfig,
+    pub cooldown: CooldownConfig,
+    pub rate_limit: RateLimitConfig,
+    pub broadcast: BroadcastConfig,
+    pub snapshot: SnapshotConfig,
+}
+
+#[derive(Debug, Clone)]
+pub struct ServerConfig {
+    pub address: String,
+    pub port: u16,
+    pub enable_cors: bool,
+}
+
+#[derive(Debug, Clone)]
+pub struct CanvasConfig {
+    pub width: u32,
+    pub height: u32,
+}
+
+#[derive(Debug, Clone)]
+pub struct CooldownConfig {
+    pub placement_secs: u64,
+}
+
+#[derive(Debug, Clone)]
+pub struct RateLimitConfig {
+    pub burst_size: u32,
+    pub per_second: u64,
+}
+
+#[derive(Debug, Clone)]
+pub struct BroadcastConfig {
+    pub channel_capacity: usize,
+}
+
+#[derive(Debug, Clone)]
+pub struct SnapshotConfig {
+    pub enabled: bool,
+    pub interval_secs: u64,
+    pub max_snapshots: usize,
+    pub directory: String,
+}
+
+pub trait ConfigSource {
+    fn load(&self) -> Result<AppConfig, ConfigError>;
+}