feat(docker): add healthcheck and wget dependency

Adds a healthcheck endpoint and updates Dockerfile/README
to include wget and define healthcheck logic.

lib/server/server.go

@@ -48,6 +48,7 @@ func Run(addr string) error {
 	router.SetHTMLTemplate(htmlTemplates)
 
 	routing.Register(router, routing.Handlers{
+		Health:             app.handleHealth,
 		Index:              app.handleIndex,
 		ShowBox:            app.handleShowBox,
 		BoxLogin:           handleBoxLogin,
@@ -114,3 +115,9 @@ func applyBoxstoreRuntimeConfig(cfg *config.Config) {
 	boxstore.SetUploadRoot(cfg.UploadsDir)
 	boxstore.SetOneTimeDownloadExpiry(cfg.OneTimeDownloadExpirySeconds)
 }
+
+func (app *App) handleHealth(c *gin.Context) {
+	c.JSON(200, gin.H{
+		"status": "healthy",
+	})
+}