[QualGroup] Add August and September 2025 slides and unify Meeting Materials

[uwendi]

This patch updates the Qualification WG documentation to:

• Add PDF slide decks for the August and September 2025 sync-up meetings
• Merge the "Meeting Minutes" and "Presentation Slides" sections into a unified "Meeting Materials" section
• Clarify that agendas and minutes are all published in the Discourse thread
• Temporarily link to slide files in llvm/docs/qual-wg/slides/
• Mention that a future patch will migrate these slide files to the llvm-www repository, once a suitable hosting location is confirmed with the community (e.g. per discussion with @nikic in [QualGroup] Add slides and documentation updates after July 2025 sync-up #147196).

[uwendi]

@nikic following up on your earlier feedback about slide hosting. This PR adds the August and September 2025 slides and merges the Meeting Minutes and Slides sections into a unified “Meeting Materials” section.

Slides are still temporarily stored under llvm/docs/qual-wg/slides/, but I’ve added a note that we’ll migrate them to llvm-www once the appropriate location is confirmed. Would appreciate your thoughts on whether creating a subfolder qual-wg in llvm-www would be suitable for that purpose.

[uwendi]

@evodius96 @petar-jovanovic tagging you for visibility and review.

[nikic]

@llvm/infrastructure-area-team Maybe the infrastructure team can provide some input on where to host your slides. I'm pretty sure it should be in llvm-www rather than llvm-project, but I can't comment on the specifics.

[CarlosAndresRamirez]

Looks good to me, it is a simple change - but I do not have the rights to approve.
Can anyone help us review/approve this?
Thank you.

[evodius96]

LGTM - do you need help merging this?

[uwendi]

Thanks for your reviews @CarlosAndresRamirez and @evodius96.
Yes, I need help merging this PR. Thanks you very much in advance!