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/handlers/settings.go

@@ -0,0 +1,54 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"prompt-generator/internal/db"
+	"prompt-generator/internal/models"
+)
+
+func GetSettings(w http.ResponseWriter, r *http.Request) {
+	settings := models.Settings{
+		LLMAPIBaseURL: cfg.LLMAPIBaseURL,
+		LLMModelName:  cfg.LLMModelName,
+	}
+	success(w, settings)
+}
+
+func UpdateSettings(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		LLMAPIBaseURL string `json:"llm_api_base_url"`
+		LLMAPIKey     string `json:"llm_api_key"`
+		LLMModelName  string `json:"llm_model_name"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		fail(w, 400, "请求格式错误")
+		return
+	}
+
+	// Update in-memory config
+	if req.LLMAPIBaseURL != "" {
+		cfg.LLMAPIBaseURL = req.LLMAPIBaseURL
+	}
+	if req.LLMModelName != "" {
+		cfg.LLMModelName = req.LLMModelName
+	}
+	if req.LLMAPIKey != "" {
+		cfg.LLMAPIKey = req.LLMAPIKey
+	}
+
+	// Persist to database (use a simple key-value table)
+	db.DB.Exec(`CREATE TABLE IF NOT EXISTS settings (
+		key_name varchar(64) NOT NULL PRIMARY KEY,
+		value text NOT NULL
+	) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4`)
+
+	db.DB.Exec("REPLACE INTO settings (key_name, value) VALUES (?, ?)", "llm_api_base_url", cfg.LLMAPIBaseURL)
+	db.DB.Exec("REPLACE INTO settings (key_name, value) VALUES (?, ?)", "llm_model_name", cfg.LLMModelName)
+	if req.LLMAPIKey != "" {
+		db.DB.Exec("REPLACE INTO settings (key_name, value) VALUES (?, ?)", "llm_api_key", cfg.LLMAPIKey)
+	}
+
+	success(w, nil)
+}