chore: remove unused artifacts directory - #53436

Why the change

artifacts/glm52-rise-video is a standalone Remotion project that renders short videos from OpenCode Go usage data, such as the GLM-5.2 launch chart and June totals. 16815473a4 added it, and it is about 8 MB, almost all of it rendered mp4s under out/. Nothing in the repo uses it.

Special things to note

• It isn't a workspace, and no file outside it references its paths. The only later commits to it are a Prettier pass in a09447bc9b and an SST-generated sst-env.d.ts in d0ba538924.
• The root .gitignore now ignores /artifacts/, so renders and screenshots written there stay local.
• The project stays in history at 16815473a4.
• A matching PR removes the folder from v2, where agent PRs also committed screenshots into it. Both branches delete the same files and add the same .gitignore line, so the next dev into v2 merge stays clean.

Verification

The pre-push bun typecheck passes.