Add Devcontainer Support for LaunchMap

[SakshayMahna]

Goal

Set up a .devcontainer/ environment so contributors can:

• Run the parser & visualizer without installing ROS 2 locally.
• Execute all tests (parser + Playwright).
• Generate and update Playwright snapshots in a consistent Linux environment, avoiding OS rendering differences.

Acceptance Criteria

• Create .devcontainer/devcontainer.json and Dockerfile with:
  • Python (parser)
  • Node.js + npm (frontend)
  • Playwright dependencies including browsers preinstalled (npx playwright install --with-deps)
  • System libraries for consistent rendering (fonts, GTK, ffmpeg, etc.)
  • ROS 2 minimal dependencies for parser tests
  • ruff and eslint for linting
  • Ensure running tests in CONTRIBUTING.md works without extra steps.
  • Document how to generate Playwright snapshots inside the container.

Sub-Tasks

• Create .devcontainer/devcontainer.json with extensions & settings
• Create Dockerfile with all parser + frontend + Playwright deps
• Preinstall Playwright browsers (chromium, firefox, webkit)
• Document usage in CONTRIBUTING.md (open in container, run tests, generate snapshots)

Notes for Contributors

• The Devcontainer will run on a Linux base, so snapshots generated here will match CI output.
• This environment will eventually be the recommended way to update Playwright snapshots.