admin → RBAC group migration: grant-based access replaces role check

surface.admin.access permission + seeded Admins system group replaces
hardcoded role == "admin" middleware checks. Admin bypass removed from
RequirePermission — all permissions flow through group membership.
Bootstrap, seed, OIDC, and admin handlers sync group membership on
role changes. Demotion/deletion safeguards use group member count.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/middleware/page_auth.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/gin-gonic/gin"
 
+	"switchboard-core/auth"
 	"switchboard-core/config"
 	"switchboard-core/database"
 	"switchboard-core/store"
@@ -85,12 +86,13 @@ func AuthOrRedirect(cfg *config.Config, users store.UserStore, cache *UserStatus
 	}
 }
 
-// RequireAdminPage aborts with 403 if the user isn't an admin.
+// RequireAdminPage aborts with 403 if the user lacks surface.admin.access.
 // Use after AuthOrRedirect for admin-only page routes.
-func RequireAdminPage() gin.HandlerFunc {
+func RequireAdminPage(stores store.Stores) gin.HandlerFunc {
 	return func(c *gin.Context) {
-		role, _ := c.Get("role")
-		if role != "admin" {
+		userID := c.GetString("user_id")
+		perms, err := resolveAndCachePerms(c, stores, userID)
+		if err != nil || !perms[auth.PermSurfaceAdminAccess] {
 			c.String(http.StatusForbidden, "Admin access required")
 			c.Abort()
 			return