feat: Archivum skeleton — Go/GraphQL backend + Vue 3 PWA frontend

Full project scaffold: multi-stage Dockerfile (ARM64/AMD64), AsciiDoc↔TipTap
bridge, Setup Wizard, CodeMirror source editor, Git-backed storage layer,
LDAP+JWT auth skeleton, Tailwind mobile-first layout, and VS Code build/push
tasks targeting registry at 192.168.0.19:5000.

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

backend/internal/config/config.go

@@ -0,0 +1,61 @@
+package config
+
+import (
+	"encoding/json"
+	"errors"
+	"os"
+)
+
+// Config holds all backend runtime configuration.
+type Config struct {
+	StoragePath string     `json:"storage_path"`
+	DBPath      string     `json:"db_path"`
+	LDAP        LDAPConfig `json:"ldap"`
+	JWTSecret   string     `json:"jwt_secret"`
+	ListenAddr  string     `json:"listen_addr"`
+}
+
+type LDAPConfig struct {
+	Host         string `json:"host"`
+	Port         int    `json:"port"`
+	BaseDN       string `json:"base_dn"`
+	BindDN       string `json:"bind_dn"`
+	BindPassword string `json:"bind_password"`
+}
+
+// ErrRequireSetup is returned when config is missing or empty,
+// signalling that the frontend should start the Setup Wizard.
+var ErrRequireSetup = errors.New("REQUIRE_SETUP")
+
+func Load(path string) (*Config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return nil, ErrRequireSetup
+		}
+		return nil, err
+	}
+
+	var cfg Config
+	if err := json.Unmarshal(data, &cfg); err != nil {
+		return nil, err
+	}
+
+	if cfg.StoragePath == "" || cfg.JWTSecret == "" {
+		return nil, ErrRequireSetup
+	}
+
+	if cfg.ListenAddr == "" {
+		cfg.ListenAddr = ":4000"
+	}
+
+	return &cfg, nil
+}
+
+func Save(path string, cfg *Config) error {
+	data, err := json.MarshalIndent(cfg, "", "  ")
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(path, data, 0600)
+}