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/auth.go

@@ -0,0 +1,69 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"prompt-generator/internal/auth"
+	"prompt-generator/internal/config"
+	"prompt-generator/internal/models"
+)
+
+var cfg *config.Config
+
+func Init(c *config.Config) {
+	cfg = c
+}
+
+func writeJSON(w http.ResponseWriter, code int, resp models.APIResponse) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(code)
+	json.NewEncoder(w).Encode(resp)
+}
+
+func success(w http.ResponseWriter, data interface{}) {
+	writeJSON(w, http.StatusOK, models.APIResponse{Code: 0, Message: "success", Data: data})
+}
+
+func fail(w http.ResponseWriter, httpCode int, msg string) {
+	writeJSON(w, httpCode, models.APIResponse{Code: httpCode, Message: msg})
+}
+
+func Login(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		Password string `json:"password"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		fail(w, 400, "请求格式错误")
+		return
+	}
+
+	if req.Password != cfg.AuthPassword {
+		fail(w, 401, "密码错误")
+		return
+	}
+
+	session, _ := auth.Store.Get(r, "session")
+	session.Values["authenticated"] = true
+	session.Save(r, w)
+
+	success(w, nil)
+}
+
+func Logout(w http.ResponseWriter, r *http.Request) {
+	session, _ := auth.Store.Get(r, "session")
+	session.Values["authenticated"] = false
+	session.Options.MaxAge = -1
+	session.Save(r, w)
+	success(w, nil)
+}
+
+func AuthCheck(w http.ResponseWriter, r *http.Request) {
+	session, _ := auth.Store.Get(r, "session")
+	authed, ok := session.Values["authenticated"].(bool)
+	if !ok || !authed {
+		fail(w, 401, "未登录")
+		return
+	}
+	success(w, map[string]bool{"authenticated": true})
+}