Add Gitea restart workflow and link-style "Run again" for the public view

The server deployment cannot mount the Docker socket safely, so the web
view's button now opens the Gitea page for a workflow_dispatch workflow
that recreates the stack and replays the demo. Gitea handles who may run it.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docker/viewer/main.go

@@ -45,7 +45,10 @@ var (
 	logDir = "/logs"
 	// The restart button needs the Docker socket; it is only enabled when the deployment says so.
 	restartEnabled = os.Getenv("RESTART_ENABLED") == "1"
-	re             = regexp.MustCompile(`^(\d\d:\d\d:\d\d\.\d{3}) \[([a-z-]+)\] (.*)$`)
+	// Without the Docker socket the page can still offer "Run again" as a link to this URL (the
+	// Gitea page that runs the restart workflow); Gitea then does the authentication.
+	restartURL = os.Getenv("RESTART_URL")
+	re         = regexp.MustCompile(`^(\d\d:\d\d:\d\d\.\d{3}) \[([a-z-]+)\] (.*)$`)
 )
 
 // tail remembers how far a file has been read and any incomplete last line.
@@ -294,7 +297,7 @@ func main() {
 		json.NewEncoder(w).Encode(lines)
 	})
 	http.HandleFunc("/api/config", func(w http.ResponseWriter, r *http.Request) {
-		json.NewEncoder(w).Encode(map[string]bool{"restart": restartEnabled})
+		json.NewEncoder(w).Encode(map[string]any{"restart": restartEnabled, "restartUrl": restartURL})
 	})
 	http.HandleFunc("/api/restart", func(w http.ResponseWriter, r *http.Request) {
 		if !restartEnabled {