feat: init sproutclaw-web — Go+Gin backend + React frontend

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/services/system_prompt.go

@@ -0,0 +1,17 @@
+package services
+
+import "os"
+
+// ReadSystemPrompt reads AGENTS.md content.
+func ReadSystemPrompt(path string) (string, error) {
+	data, err := os.ReadFile(path)
+	if os.IsNotExist(err) {
+		return "", nil
+	}
+	return string(data), err
+}
+
+// WriteSystemPrompt writes AGENTS.md content.
+func WriteSystemPrompt(path, content string) error {
+	return os.WriteFile(path, []byte(content), 0o644)
+}