Move Zapier link from connections list to user menu (SaaS only) and lazy-load SDK (#1536)

- Remove Zapier link and SVG logos from connections list
- Add Zapier menu item to both desktop dropdown and mobile sidebar menus, gated behind isSaas
- Remove global Zapier SDK script/CSS from index.html and index.saas.html
- Dynamically load Zapier SDK in ZapierComponent on init
- Migrate Zapier component to signals and @if template syntax

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: gugu

frontend/src/app/app.component.html

@@ -42,6 +42,12 @@
                 </mat-icon>
                 <div matListItemTitle>Secrets</div>
             </a>
+            <a mat-list-item *ngIf="isSaas" routerLink="/zapier" data-testid="zapier-link-account-menu">
+                <mat-icon matListItemIcon class="connection-navigation__icon">
+                    electric_bolt
+                </mat-icon>
+                <div matListItemTitle>Zapier</div>
+            </a>
             <a mat-list-item href="https://docs.rocketadmin.com/" target="_blank">
                 <mat-icon matListItemIcon class="connection-navigation__icon" fontSet="material-icons-outlined">help_outlined</mat-icon>
                 <div matListItemTitle>Help center</div>
@@ -182,6 +188,12 @@
                         </mat-icon>
                         <span>Secrets</span>
                     </a>
+                    <a mat-menu-item *ngIf="isSaas" routerLink="/zapier" data-testid="zapier-link-account-menu">
+                        <mat-icon class="nav-menu__list-link-icon">
+                            electric_bolt
+                        </mat-icon>
+                        <span>Zapier</span>
+                    </a>
                     <a mat-menu-item href="https://docs.rocketadmin.com/" target="_blank">
                         <mat-icon fontSet="material-icons-outlined">help_outlined</mat-icon>
                         <span>Help center</span>