feat: initialize project skeleton with Go backend, database, and config

- Go module with standard library + gorilla/sessions + mysql driver
- Config: env-based configuration with .env file support
- Database: MySQL connection with auto-migration for 6 tables
- Seed data: 12 system tags with options, 8 system snippets
- Auth: session cookie middleware
- Handlers: auth, tags, snippets, builder, claude, dashboard, suggestions, settings
- LLM: OpenAI-compatible client with 30s timeout
- Docker: Dockerfile + docker-compose.yml
- .env.example with all configuration options

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

internal/config/config.go

@@ -0,0 +1,42 @@
+package config
+
+import (
+	"os"
+)
+
+type Config struct {
+	ServerPort    string
+	SessionSecret string
+	DBHost        string
+	DBPort        string
+	DBUser        string
+	DBPassword    string
+	DBName        string
+	AuthPassword  string
+	LLMAPIBaseURL string
+	LLMAPIKey     string
+	LLMModelName  string
+}
+
+func Load() *Config {
+	return &Config{
+		ServerPort:    getEnv("SERVER_PORT", "8080"),
+		SessionSecret: getEnv("SESSION_SECRET", "default-secret-change-me"),
+		DBHost:        getEnv("DB_HOST", "127.0.0.1"),
+		DBPort:        getEnv("DB_PORT", "3306"),
+		DBUser:        getEnv("DB_USER", "root"),
+		DBPassword:    getEnv("DB_PASSWORD", ""),
+		DBName:        getEnv("DB_NAME", "prompt_generator"),
+		AuthPassword:  getEnv("AUTH_PASSWORD", "admin"),
+		LLMAPIBaseURL: getEnv("LLM_API_BASE_URL", "https://api.deepseek.com/v1"),
+		LLMAPIKey:     getEnv("LLM_API_KEY", ""),
+		LLMModelName:  getEnv("LLM_MODEL_NAME", "deepseek-chat"),
+	}
+}
+
+func getEnv(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}