Docs: create first public simulation media pack plan

[vultrdev]

Objective

Prepare the first public media/storytelling layer so the simulation can become content as soon as it looks real enough.

Scope

• tighten the demo video plan
• define teaser/walkthrough/replay cuts
• specify what each first video must prove
• keep claims honest about current maturity

References

• agentarium-docs/media/README.md
• agentarium-docs/docs/project/demo-video-plan.md

Done when

• there is a clear first-wave media checklist ready for capture
• docs stay aligned with the real product state