chore(devcontainer): consolidate and simplify dev/test/ci envs

[solnic]

This unifies our dev/test/ci dev container setup:

• Removes reliance on docker compose - required services now run inside containers, this is just simpler and does not cause port conflicts on dev machines.
• Uses latest Ubuntu LTS images as the base (and old LTS for Ruby 2.7.
• Uses mise for Ruby installation exclusively.
• Uses a custom local dev container feature for installing our entire toolchain (baked into image for faster startups).
• Drops dependency on playwright (we only used it for chromium installation and its deps, for running e2e specs we actually use Capybara over here).
• Removes run script as the entrypoint - no longer needed.
• Adds ci-run as a simpler wrapper script for executing e2e specs on CI.
• Simplifies devcontainer config by using default workspace dir path.

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

Want reviews to match your repository better? Bugbot Learning can learn team-specific rules from PR activity. A team admin can enable Learning in the Cursor dashboard.

^{Reviewed by Cursor Bugbot for commit 2a2c499. Configure here.}