feat(terminal): add clipboard paste support for text and images

- Custom index.html with xterm.js for reliable Ctrl+V text paste
- Go clipboard-upload service saves pasted images to /tmp/clipboard-images/
- Traefik IngressRoute routes /clipboard/* to upload service (same-origin)
- Authentik-protected upload path with strip-prefix middleware

stacks/terminal/clipboard-upload/go.mod

@@ -0,0 +1,3 @@
+module clipboard-upload
+
+go 1.25.0

stacks/terminal/clipboard-upload/main.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+const (
+	uploadDir  = "/tmp/clipboard-images"
+	maxUpload  = 10 << 20 // 10MB
+	listenAddr = "0.0.0.0:7683"
+)
+
+func main() {
+	if err := os.MkdirAll(uploadDir, 0755); err != nil {
+		log.Fatalf("Failed to create upload dir: %v", err)
+	}
+
+	http.HandleFunc("/upload", handleUpload)
+	http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte("ok"))
+	})
+
+	log.Printf("Clipboard upload service listening on %s, saving to %s", listenAddr, uploadDir)
+	log.Fatal(http.ListenAndServe(listenAddr, nil))
+}
+
+func handleUpload(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "POST only", http.StatusMethodNotAllowed)
+		return
+	}
+
+	r.Body = http.MaxBytesReader(w, r.Body, maxUpload)
+	if err := r.ParseMultipartForm(maxUpload); err != nil {
+		http.Error(w, "File too large (max 10MB)", http.StatusRequestEntityTooLarge)
+		return
+	}
+
+	file, header, err := r.FormFile("image")
+	if err != nil {
+		http.Error(w, "Missing 'image' field", http.StatusBadRequest)
+		return
+	}
+	defer file.Close()
+
+	ct := header.Header.Get("Content-Type")
+	if !strings.HasPrefix(ct, "image/") {
+		http.Error(w, "Not an image", http.StatusBadRequest)
+		return
+	}
+
+	ext := ".png"
+	switch ct {
+	case "image/jpeg":
+		ext = ".jpg"
+	case "image/gif":
+		ext = ".gif"
+	case "image/webp":
+		ext = ".webp"
+	}
+
+	randBytes := make([]byte, 4)
+	rand.Read(randBytes)
+	filename := fmt.Sprintf("%s-%s%s", time.Now().Format("20060102-150405"), hex.EncodeToString(randBytes), ext)
+	destPath := filepath.Join(uploadDir, filename)
+
+	dest, err := os.Create(destPath)
+	if err != nil {
+		http.Error(w, "Failed to save", http.StatusInternalServerError)
+		return
+	}
+	defer dest.Close()
+
+	if _, err := io.Copy(dest, file); err != nil {
+		os.Remove(destPath)
+		http.Error(w, "Failed to save", http.StatusInternalServerError)
+		return
+	}
+
+	log.Printf("Saved clipboard image: %s (%s, %d bytes)", destPath, ct, header.Size)
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(map[string]string{"path": destPath})
+}