chore: update vscode devcontainer and fix tests in devcontainer

[KiTTYsh]

What

• Remove devcontainer Dockerfile and use container directly from compose.yml
• Bump devcontainer image version
• Install ffmpeg during devcontainer initialization, change default devcontainer hostname to cherrypick.local
• Add vscode launch/build shortcuts to vscode profile

Why

• Removing Dockerfile removes unnecessary build operation
• Keeping environment up to date speeds up dependency installation during devcontainer initialization
• Ffmpeg and default hostname changes fix testing inside of devcontainer
• Launch/build shortcuts for convenience

Additional info (optional)

Previous node devcontainer was built in 2023, and the proposed image was updated yesterday. The new image keeps the same NodeJS version.

These changes only affect the development environment in vscode, and do not change any project code or build artifacts.

Checklist

• [✅] Read the contribution guide
• [✅] Test working in a local environment
• [❌] (If needed) Update CHANGELOG_CHERRYPICK.md
• [❌] (If possible) Add tests