Add CI workflow to compress media assets

[MUFFANUJ]

Problem

Media assets (GIFs, MP4s, PNGs) in the repo are uncompressed, currently totalling ~16-17MB.
These get heavier over time as examples are added/updated

Proposed Solution

Add a GitHub Actions workflow that:

• Compresses all existing and future PNGs, GIFs, and MP4s via CI
• Runs automatically on push to main when media files change
• Can be triggered manually (workflow_dispatch) to compress all existing assets

Compression happens at CI time, not runtime, and the bot commits the compressed files back.

Additional context

• Discussed in Bundle extension examples in PyPI installs plugin-playground#105

[krassowski]

Runs automatically on push to main when media files change

I think we should not do that due to security implications. Instead, on PRs we should:

• compress assets
• upload the ones which changed upon compression (as an artifact)
• fail the workflow if any changed