feat: initial blog engine with multi-language, profile, and role system

- Gin + GORM + Tailwind CSS blog engine
- OS-aware config (Linux /etc/blog_go/, Windows ./win/etc/blog_go/)
- SQLite by default, MySQL support via config
- Auto-migrate database + seed admin user on first run
- Session-based auth (login/logout)
- i18n: Chinese/English with auto-detect + manual switch
- Avatar dropdown nav with click-to-toggle menu
- Profile page: avatar upload, edit info, change password
- Role system: admin (full access) and author (profile only)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

config/config.go

@@ -0,0 +1,125 @@
+package config
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"runtime"
+
+	"gopkg.in/yaml.v3"
+)
+
+// Config holds all application configuration.
+type Config struct {
+	Database DatabaseConfig `yaml:"database"`
+	Port     string         `yaml:"port"`
+	Path     string         `yaml:"path"`
+	Secret   string         `yaml:"secret"`
+}
+
+// DatabaseConfig holds database-specific configuration.
+type DatabaseConfig struct {
+	Type string `yaml:"type"` // "sqlite" (default) or "mysql"
+	DSN  string `yaml:"dsn"`  // MySQL connection string (ignored for sqlite)
+}
+
+// defaultPort is the fallback web server port.
+const defaultPort = "8080"
+
+// getConfigPath returns the OS-aware config directory and config file path.
+func getConfigPath() (dir, file string) {
+	if runtime.GOOS == "windows" {
+		dir = filepath.Join(".", "win", "etc", "blog_go")
+	} else {
+		dir = filepath.Join("/", "etc", "blog_go")
+	}
+	file = filepath.Join(dir, "config.yaml")
+	return
+}
+
+// getDefaultStoragePath returns the OS-aware default storage path.
+func getDefaultStoragePath() string {
+	if runtime.GOOS == "windows" {
+		return filepath.Join(".", "win", "srv", "blog_go")
+	}
+	return filepath.Join("/", "srv", "blog_go")
+}
+
+// generateSecret returns a random-ish hex string for the session secret.
+func generateSecret() string {
+	// Use a combination of hostname + random to produce a unique secret.
+	hostname, _ := os.Hostname()
+	input := fmt.Sprintf("%s-%d", hostname, os.Getpid())
+	hash := sha256.Sum256([]byte(input))
+	return fmt.Sprintf("%x", hash)
+}
+
+// LoadConfig reads the config file or creates one with defaults.
+func LoadConfig() *Config {
+	configDir, configFile := getConfigPath()
+	defaultPath := getDefaultStoragePath()
+
+	cfg := &Config{}
+
+	// Check if config file exists; create with defaults if not.
+	if _, err := os.Stat(configFile); os.IsNotExist(err) {
+		log.Printf("Config file not found at %s, creating with defaults...", configFile)
+		if err := os.MkdirAll(configDir, 0755); err != nil {
+			log.Fatalf("Failed to create config directory %s: %v", configDir, err)
+		}
+
+		cfg = &Config{
+			Database: DatabaseConfig{
+				Type: "sqlite",
+				DSN:  "",
+			},
+			Port:   defaultPort,
+			Path:   defaultPath,
+			Secret: generateSecret(),
+		}
+
+		data, err := yaml.Marshal(cfg)
+		if err != nil {
+			log.Fatalf("Failed to marshal default config: %v", err)
+		}
+
+		if err := os.WriteFile(configFile, data, 0644); err != nil {
+			log.Fatalf("Failed to write config file %s: %v", configFile, err)
+		}
+		log.Printf("Default config created at %s", configFile)
+		return cfg
+	}
+
+	// Read existing config file.
+	data, err := os.ReadFile(configFile)
+	if err != nil {
+		log.Printf("Warning: could not read config file %s: %v, using defaults", configFile, err)
+		return applyDefaults(cfg, defaultPath)
+	}
+
+	if err := yaml.Unmarshal(data, cfg); err != nil {
+		log.Printf("Warning: malformed config file %s: %v, using defaults", configFile, err)
+		cfg = &Config{}
+	}
+
+	return applyDefaults(cfg, defaultPath)
+}
+
+// applyDefaults fills zero-value fields with sensible defaults.
+func applyDefaults(cfg *Config, defaultPath string) *Config {
+	if cfg.Port == "" {
+		cfg.Port = defaultPort
+	}
+	if cfg.Database.Type == "" {
+		cfg.Database.Type = "sqlite"
+	}
+	if cfg.Path == "" {
+		cfg.Path = defaultPath
+	}
+	if cfg.Secret == "" {
+		cfg.Secret = generateSecret()
+	}
+	return cfg
+}