Upgrade Angular 20.3.9 to 20.3.18

Patch-level upgrade. Includes CVE-2025-59052 security fix (SSR),
iframe src sanitization, and translated attribute sanitization.
No breaking change impact — Stratos does not use the affected
bootstrapApplication/getPlatform/destroyPlatform APIs.

Vitest: 1029 passed, 5 pre-existing errors unchanged.
Playwright: 6 passed, 0 failed.

Also fix about-page E2E fixture name to connectedEndpointsAdminPage.

FWT-839

Author: norman-abramovitz