Initial open-source release (MIT): image2api AI gateway

Full Go backend + Vue 3 frontend, OpenAI-compatible API, multi-provider
account pools, billing/admin, Docker one-command deploy with auto HTTPS.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/internal/service/alphabet.go

@@ -0,0 +1,20 @@
+package service
+
+import nanoid "github.com/matoous/go-nanoid/v2"
+
+const UpperAlphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+func randomUpper(n int) string {
+	v, err := nanoid.Generate(UpperAlphabet, n)
+	if err != nil {
+		if n <= 0 {
+			return ""
+		}
+		out := make([]byte, n)
+		for i := range out {
+			out[i] = 'A'
+		}
+		return string(out)
+	}
+	return v
+}