add slides + embed recording for EESSI-as-a-base-stack webinar

Author: Richard Top

docs/training-events/2026/EESSI-webinars-spring-2026-EESSI-as-a-base-stack-2026-06-01.pdf

@@ -160,13 +160,18 @@ The presentation will cover EESSI's architecture, its integration with establish
 
 ---
 
-
 ### Using EESSI as a base for a central software stack
 
 - Monday 1 June 2026, 14:00-16:00 CEST (Zoom webinar)
 - speakers:
     - Caspar van Leeuwen (SURF)
     - Bob Dröge (University of Groningen)
+- [slides (PDF)](EESSI-webinars-spring-2026-EESSI-as-a-base-stack-2026-06-01.pdf)
+- [recording (YouTube)](https://youtu.be/WCQ2vEnQon4)
+
+<div align="center">
+<iframe width="560" height="315" src="https://www.youtube.com/embed/WCQ2vEnQon4?si=9I_s31nOD1s2jZE0" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
+</div>
 
 #### Outline
 
@@ -180,9 +185,6 @@ The presentation will cover EESSI's architecture, its integration with establish
 
 #### Materials {: #materials-cvmfs }
 
-- slides (PDF) coming soon!
-- recording (YouTube) coming soon!
-
 ---
 
 !!! tip

docs/training-events/2026/webinar-series-2026Q2.md

@@ -3,6 +3,9 @@
 ## Upcoming events (2026)
 
 * [*EESSI happy hour sessions 2026*](./happy-hours-sessions.md) (online sessions **every** Monday, starting 12 January 2026)
+
+### Past events (2026)
+
 * [*EESSI webinar series (April-May 2026)*](2026/webinar-series-2026Q2.md) (online tutorials)
     * [**Introduction to EESSI** *(27 April 2026)*](2026/webinar-series-2026Q2.md#introduction-to-eessi)
     * [**Building software on top of EESSI + contributing to EESSI** *(4 May 2026)*](2026/webinar-series-2026Q2.md#building-software-on-top-of-eessi-contributing-to-eessi)