[Notebook Migration] Add Jupyter notebook iframe panel component

[zyratlo]

Task Summary

Introduce JupyterNotebookPanelComponent, the draggable iframe shell that hosts JupyterLab inside the Texera workspace.

Scope

Adds and modifies these files:

• frontend/src/app/workspace/component/jupyter-notebook-panel/jupyter-notebook-panel.component.ts
  • JupyterNotebookPanelComponent
    • ngOnInit subscribes to jupyterPanelService.jupyterNotebookPanelVisible$; on each emission it sets isVisible, and when visibility flips to true it fetches the iframe URL from notebookMigrationService.getJupyterIframeURL(), runs it through DomSanitizer.bypassSecurityTrustResourceUrl, and updates iframeRef
    • ngAfterViewInit registers the iframe with the panel service via setIframeRef
    • closePanel() calls jupyterPanelService.closeJupyterNotebookPanel()
    • minimizePanel() calls jupyterPanelService.minimizeJupyterNotebookPanel().
• frontend/src/app/workspace/component/jupyter-notebook-panel/jupyter-notebook-panel.component.html
  • cdkDrag-enabled panel with header (title + close/minimize buttons; close uses nz-popconfirm for a "delete" confirmation)
  • <iframe [src]="jupyterUrl"> body bound to the sanitized URL, gated on *ngIf="isVisible".
• frontend/src/app/workspace/component/jupyter-notebook-panel/jupyter-notebook-panel.component.scss
  • fixed-position panel styling, drag handle visuals, iframe sizing.
• frontend/src/app/workspace/component/jupyter-notebook-panel/jupyter-notebook-panel.component.spec.ts
• frontend/src/app/app.module.ts (+2 lines)
  • imports JupyterNotebookPanelComponent and adds it to the @NgModule.declarations array.

Task Type

• Refactor / Cleanup
• DevOps / Deployment / CI
• Testing / QA
• Documentation
• Performance
• Other

[zyratlo]

/parent-issue #4301