feat(PROJ-17): Admin Dashboard Systemauslastung immer anzeigen

- Systemauslastungs-Sektion wird immer gerendert (nicht nur bei Erfolg)
- Fehlermeldung wenn /api/admin/system/stats nicht erreichbar ist
- Feature-Status auf In Review gesetzt

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

config/config.go

@@ -0,0 +1,100 @@
+package config
+
+import (
+	"fmt"
+	"os"
+
+	"gopkg.in/yaml.v3"
+)
+
+// APIConfig holds configuration for the HTTP API server.
+type APIConfig struct {
+	Bind   string `yaml:"bind"`
+	Secret string `yaml:"secret"`
+}
+
+// Config is the full application configuration loaded from YAML.
+type Config struct {
+	Server   ServerConfig   `yaml:"server"`
+	Storage  StorageConfig  `yaml:"storage"`
+	Database DatabaseConfig `yaml:"database"`
+	SMTP     SMTPConfig     `yaml:"smtp"`
+	API      APIConfig      `yaml:"api"`
+	Index    IndexConfig    `yaml:"index"`
+	Audit    AuditConfig    `yaml:"audit"`
+	Logging  LoggingConfig  `yaml:"logging"`
+}
+
+// ServerConfig holds port settings for the main services.
+type ServerConfig struct {
+	APIPort  int `yaml:"api_port"`
+	SMTPPort int `yaml:"smtp_port"`
+}
+
+// StorageConfig holds file system paths for email storage.
+type StorageConfig struct {
+	StorePath  string `yaml:"store_path"`
+	AStorePath string `yaml:"astore_path"`
+	XapianPath string `yaml:"xapian_path"`
+	Keyfile    string `yaml:"keyfile"`
+}
+
+// DatabaseConfig holds PostgreSQL connection settings.
+type DatabaseConfig struct {
+	Host     string `yaml:"host"`
+	Port     int    `yaml:"port"`
+	Name     string `yaml:"name"`
+	User     string `yaml:"user"`
+	Password string `yaml:"password"`
+	SSLMode  string `yaml:"sslmode"`
+}
+
+// DSN builds a PostgreSQL connection string from the config fields.
+func (d DatabaseConfig) DSN() string {
+	return fmt.Sprintf("postgres://%s:%s@%s:%d/%s?sslmode=%s",
+		d.User, d.Password, d.Host, d.Port, d.Name, d.SSLMode)
+}
+
+// SMTPConfig holds settings for the embedded SMTP server.
+type SMTPConfig struct {
+	Enabled    bool     `yaml:"enabled"`
+	Bind       string   `yaml:"bind"`
+	Domain     string   `yaml:"domain"`
+	TLSCert    string   `yaml:"tls_cert"`
+	TLSKey     string   `yaml:"tls_key"`
+	MaxSizeMB  int      `yaml:"max_size_mb"`
+	AllowedIPs []string `yaml:"allowed_ips"`
+}
+
+// IndexConfig holds full-text index settings.
+type IndexConfig struct {
+	Path           string `yaml:"path"`
+	Backend        string `yaml:"backend"`
+	BatchSize      int    `yaml:"batch_size"`
+	AsyncQueueSize int    `yaml:"async_queue_size"`
+}
+
+// AuditConfig holds audit log settings.
+type AuditConfig struct {
+	LogPath       string `yaml:"log_path"`
+	RetentionDays int    `yaml:"retention_days"`
+}
+
+// LoggingConfig holds application logging settings.
+type LoggingConfig struct {
+	Path  string `yaml:"path"`
+	Level string `yaml:"level"`
+}
+
+// Load reads a YAML config file from path and returns a parsed Config.
+func Load(path string) (*Config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	var cfg Config
+	if err := yaml.Unmarshal(data, &cfg); err != nil {
+		return nil, err
+	}
+	return &cfg, nil
+}