feat(auth): implement master key authentication system with child key issuance

Add admin and master authentication layers with JWT support. Replace direct
key creation with hierarchical master/child key system. Update database
schema to support master accounts with configurable limits and epoch-based
key revocation. Add health check endpoint with system status monitoring.

BREAKING CHANGE: Removed direct POST /keys endpoint in favor of master-based
key issuance through /v1/tokens. Database migration requires dropping old User
table and creating Master table with new relationships.

internal/api/admin_handler.go

@@ -0,0 +1,54 @@
+package api
+
+import (
+	"net/http"
+
+	"github.com/ez-api/ez-api/internal/service"
+	"github.com/gin-gonic/gin"
+)
+
+type AdminHandler struct {
+	masterService *service.MasterService
+}
+
+func NewAdminHandler(masterService *service.MasterService) *AdminHandler {
+	return &AdminHandler{masterService: masterService}
+}
+
+type CreateMasterRequest struct {
+	Name         string `json:"name" binding:"required"`
+	Group        string `json:"group" binding:"required"`
+	MaxChildKeys int    `json:"max_child_keys"`
+	GlobalQPS    int    `json:"global_qps"`
+}
+
+func (h *AdminHandler) CreateMaster(c *gin.Context) {
+	var req CreateMasterRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	// Use defaults if not provided
+	if req.MaxChildKeys == 0 {
+		req.MaxChildKeys = 5
+	}
+	if req.GlobalQPS == 0 {
+		req.GlobalQPS = 3
+	}
+
+	master, rawMasterKey, err := h.masterService.CreateMaster(req.Name, req.Group, req.MaxChildKeys, req.GlobalQPS)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create master key", "details": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusCreated, gin.H{
+		"id":             master.ID,
+		"name":           master.Name,
+		"group":          master.Group,
+		"master_key":     rawMasterKey, // Only show this on creation
+		"max_child_keys": master.MaxChildKeys,
+		"global_qps":     master.GlobalQPS,
+	})
+}