feat(backend): implement user, ACL, and audit stacks

Add UserService (GetMe, UpdateMe, admin CRUD with block/unblock),
UserHandler (/users, /users/me), ACLHandler (GET/PUT /acl/:type/:id),
AuditHandler (GET /audit with all filters). Fix UserRepo.Update to
include is_blocked. Wire all remaining routes.

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

backend/internal/handler/audit_handler.go

@@ -0,0 +1,120 @@
+package handler
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+
+	"tanabata/backend/internal/domain"
+	"tanabata/backend/internal/service"
+)
+
+// AuditHandler handles GET /audit.
+type AuditHandler struct {
+	auditSvc *service.AuditService
+}
+
+// NewAuditHandler creates an AuditHandler.
+func NewAuditHandler(auditSvc *service.AuditService) *AuditHandler {
+	return &AuditHandler{auditSvc: auditSvc}
+}
+
+// ---------------------------------------------------------------------------
+// Response type
+// ---------------------------------------------------------------------------
+
+type auditEntryJSON struct {
+	ID          int64   `json:"id"`
+	UserID      int16   `json:"user_id"`
+	UserName    string  `json:"user_name"`
+	Action      string  `json:"action"`
+	ObjectType  *string `json:"object_type"`
+	ObjectID    *string `json:"object_id"`
+	PerformedAt string  `json:"performed_at"`
+}
+
+func toAuditEntryJSON(e domain.AuditEntry) auditEntryJSON {
+	j := auditEntryJSON{
+		ID:          e.ID,
+		UserID:      e.UserID,
+		UserName:    e.UserName,
+		Action:      e.Action,
+		ObjectType:  e.ObjectType,
+		PerformedAt: e.PerformedAt.UTC().Format(time.RFC3339),
+	}
+	if e.ObjectID != nil {
+		s := e.ObjectID.String()
+		j.ObjectID = &s
+	}
+	return j
+}
+
+// ---------------------------------------------------------------------------
+// GET /audit  (admin)
+// ---------------------------------------------------------------------------
+
+func (h *AuditHandler) List(c *gin.Context) {
+	if !requireAdmin(c) {
+		return
+	}
+
+	filter := domain.AuditFilter{}
+
+	if s := c.Query("limit"); s != "" {
+		if n, err := strconv.Atoi(s); err == nil {
+			filter.Limit = n
+		}
+	}
+	if s := c.Query("offset"); s != "" {
+		if n, err := strconv.Atoi(s); err == nil {
+			filter.Offset = n
+		}
+	}
+	if s := c.Query("user_id"); s != "" {
+		if n, err := strconv.ParseInt(s, 10, 16); err == nil {
+			id := int16(n)
+			filter.UserID = &id
+		}
+	}
+	if s := c.Query("action"); s != "" {
+		filter.Action = s
+	}
+	if s := c.Query("object_type"); s != "" {
+		filter.ObjectType = s
+	}
+	if s := c.Query("object_id"); s != "" {
+		if id, err := uuid.Parse(s); err == nil {
+			filter.ObjectID = &id
+		}
+	}
+	if s := c.Query("from"); s != "" {
+		if t, err := time.Parse(time.RFC3339, s); err == nil {
+			filter.From = &t
+		}
+	}
+	if s := c.Query("to"); s != "" {
+		if t, err := time.Parse(time.RFC3339, s); err == nil {
+			filter.To = &t
+		}
+	}
+
+	page, err := h.auditSvc.Query(c.Request.Context(), filter)
+	if err != nil {
+		respondError(c, err)
+		return
+	}
+
+	items := make([]auditEntryJSON, len(page.Items))
+	for i, e := range page.Items {
+		items[i] = toAuditEntryJSON(e)
+	}
+	respondJSON(c, http.StatusOK, gin.H{
+		"items":  items,
+		"total":  page.Total,
+		"offset": page.Offset,
+		"limit":  page.Limit,
+	})
+}