Add server Timeout middleware for context-based request deadlines

Wraps http.TimeoutHandler to return 503 when handlers exceed the
configured duration. Unlike http.Server.WriteTimeout, this allows
handlers to complete gracefully via context cancellation.

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

server/middleware_timeout.go

@@ -0,0 +1,15 @@
+package server
+
+import (
+	"net/http"
+	"time"
+)
+
+// Timeout returns a middleware that limits request processing time.
+// If the handler does not complete within d, the client receives a
+// 503 Service Unavailable response. It wraps http.TimeoutHandler.
+func Timeout(d time.Duration) Middleware {
+	return func(next http.Handler) http.Handler {
+		return http.TimeoutHandler(next, d, "Service Unavailable\n")
+	}
+}