Update talks & try to fix gallery

[skzhang1]

Why are these changes needed?

1. update talks
2. config to render all previous talks
3. try to fix gallery images

Related issue number

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[qingyun-wu]

Thanks Shaokun