feat(dev): add Overmind-based development workflow

Add Procfile.dev for parallel backend/frontend development with
Overmind, replacing the sequential build approach. The new `just dev`
recipe starts both servers simultaneously with log multiplexing.

Changes:
- Update `just dev` to use Overmind
- Add `build-demo` recipe with optional Windows cross-compilation
- Add `smoke` recipe to verify development setup
- Improve logging in backend with bind address and dev mode indicator
- Allow missing Windows executable in debug builds

.gitignore

@@ -3,3 +3,4 @@
 demo-*
 /public
 .env
+.overmind.sock

Justfile

@@ -45,20 +45,63 @@ frontend-build:
     @echo "Building frontend..."
     pnpm --dir frontend build
 
-# Development server with hot reload (backend + ensures frontend is built)
-dev: frontend-build
-    @echo "Starting backend development server with bacon..."
-    @echo "Frontend is served from ./public (built from frontend/)"
-    bacon run
+# Build demo executables (debug mode for faster dev builds)
+build-demo:
+    #!/usr/bin/env bash
+    set -euo pipefail
+
+    echo "Building demo executables..."
+
+    # Always build Linux demo
+    echo "Building Linux demo..."
+    cargo build --bin demo
+    cp target/debug/demo ./demo-linux
+    echo "  [OK] Linux demo built"
+
+    # Try to build Windows demo if cross-compilation is available
+    if rustup target list --installed | grep -q x86_64-pc-windows-gnu; then
+        echo "Building Windows demo..."
+        if cargo build --bin demo --target x86_64-pc-windows-gnu 2>/dev/null; then
+            cp target/x86_64-pc-windows-gnu/debug/demo.exe ./demo.exe
+            echo "  [OK] Windows demo built"
+        else
+            echo "  [!] Windows build failed (mingw-w64 toolchain may not be installed)"
+            echo "      Continuing without Windows demo..."
+        fi
+    else
+        echo "  [SKIP] Windows target not installed"
+        echo "         Install with: rustup target add x86_64-pc-windows-gnu"
+        echo "         Also requires: sudo apt install mingw-w64"
+    fi
+
+    echo "Demo executables ready!"
+
+# Development server with hot reload (backend + frontend using Overmind)
+dev: build-demo
+    @echo "Starting development servers with Overmind..."
+    @echo ""
+    @echo "Backend will run on:  http://localhost:5800"
+    @echo "Frontend will run on: http://localhost:4321"
+    @echo ""
+    @echo "Overmind multiplexes logs with prefixes:"
+    @echo "  [backend]  - Bacon watching Rust backend"
+    @echo "  [frontend] - Astro dev server"
+    @echo ""
+    @echo "Overmind shortcuts:"
+    @echo "  Ctrl+C     - Stop all processes"
+    @echo "  'overmind connect <process>' - Attach to a specific process"
+    @echo ""
+    overmind start -f Procfile.dev
 
 # Watch backend only (for when frontend is already built)
-dev-backend:
+dev-backend: build-demo
     @echo "Starting backend watch with bacon..."
     bacon run
 
 # Watch and serve frontend only
 dev-frontend:
     @echo "Starting frontend dev server..."
+    @echo "Make sure the backend is running on port 5800!"
     pnpm --dir frontend dev
 
 # Simple development run (no hot reload)
@@ -119,3 +162,30 @@ quick: format
     @echo "Running quick clippy check..."
     cargo clippy --workspace --all-targets --all-features -- -D warnings
     @echo "Quick check completed!"
+
+# Verify dev setup is ready (builds demo executables and checks dependencies)
+smoke: build-demo
+    @echo "Verifying development setup..."
+    @echo ""
+    @echo "Checking for overmind (required for 'just dev')..."
+    @command -v overmind >/dev/null 2>&1 || { echo "  [!] overmind not found. Install from: https://github.com/DarthSim/overmind#installation"; exit 1; }
+    @echo "  [OK] overmind found"
+    @echo ""
+    @echo "Checking for bacon..."
+    @command -v bacon >/dev/null 2>&1 || { echo "  [!] bacon not found. Install with: cargo install bacon"; exit 1; }
+    @echo "  [OK] bacon found"
+    @echo ""
+    @echo "Checking for pnpm..."
+    @command -v pnpm >/dev/null 2>&1 || { echo "  [!] pnpm not found. Install from: https://pnpm.io/installation"; exit 1; }
+    @echo "  [OK] pnpm found"
+    @echo ""
+    @echo "Checking demo executables..."
+    @test -f ./demo-linux || { echo "  [!] demo-linux not found"; exit 1; }
+    @echo "  [OK] demo-linux exists"
+    @if [ -f ./demo.exe ]; then \
+        echo "  [OK] demo.exe exists"; \
+    else \
+        echo "  [SKIP] demo.exe not found (Windows builds not available)"; \
+    fi
+    @echo ""
+    @echo "[OK] Development setup is ready! Run 'just dev' to start."

Procfile.dev

@@ -0,0 +1,5 @@
+# Procfile for Overmind development workflow
+# Start with: overmind start -f Procfile.dev
+
+backend: PORT=5800 bacon run --headless
+frontend: pnpm --dir frontend dev

backend/src/main.rs

@@ -66,6 +66,16 @@ async fn main() {
         // ("MacOS", "./demo-macos"),
     ] {
         if let Err(e) = store.add_executable(exe_type, exe_path) {
+            // In debug mode, allow missing Windows executable for dev convenience
+            if cfg!(debug_assertions) && exe_type == "Windows" {
+                tracing::warn!(
+                    "Windows executable not found at {} (skipping - cross-compilation not set up)",
+                    exe_path
+                );
+                tracing::warn!("To enable Windows builds: rustup target add x86_64-pc-windows-gnu && sudo apt install mingw-w64");
+                continue;
+            }
+
             tracing::error!("{}", e);
             std::process::exit(1);
         }
@@ -105,6 +115,15 @@ async fn main() {
 
     let service = Service::new(router).hoop(cors).hoop(Logger::new());
 
-    let acceptor = TcpListener::new(config.bind_addr()).bind().await;
+    let bind_addr = config.bind_addr();
+    tracing::info!("Server starting on http://{}", bind_addr);
+    tracing::info!("WebSocket endpoint: ws://{}/ws", bind_addr);
+
+    if cfg!(debug_assertions) {
+        tracing::info!("Development mode - CORS allows all origins");
+        tracing::info!("Access the app at http://localhost:4321 (Astro dev server)");
+    }
+
+    let acceptor = TcpListener::new(&bind_addr).bind().await;
     Server::new(acceptor).serve(service).await;
 }