fix(ui): Restrict sidebar initialization to the vertical navbar

initSideNav() matched every .navbar element, and
templates/base/layout.html puts that class on both the sidebar aside and
the top header, so a second SideNav was constructed for the header.
Scope the selector to .navbar-vertical, which is what the pre-Tabler
selector .sidenav did.

Widen the sidebar element type from HTMLDivElement to HTMLElement, since
the element the selector matches is an aside.

Fixes #22929

netbox/project-static/src/sidenav.ts

@@ -10,7 +10,7 @@ class SideNav {
   /**
    * Sidenav container element.
    */
-  private base: HTMLDivElement;
+  private base: HTMLElement;
 
   /**
    * SideNav internal state manager.
@@ -27,7 +27,7 @@ class SideNav {
    */
   private sections: Section[] = [];
 
-  constructor(base: HTMLDivElement) {
+  constructor(base: HTMLElement) {
     this.base = base;
     this.state = new StateManager<NavState>(
       { pinned: true },
@@ -314,7 +314,7 @@ class SideNav {
 }
 
 export function initSideNav(): void {
-  for (const sidenav of getElements<HTMLDivElement>('.navbar')) {
+  for (const sidenav of getElements<HTMLElement>('.navbar-vertical')) {
     new SideNav(sidenav);
   }
 }