chore: Update devcontainer image version to 0.2.1

[nacholiya]

Description

Pin the devcontainer image from the floating dev tag to the stable 0.2.1 release.

This ensures reproducible development environments and avoids unexpected changes from moving tags.

Type of Change

• feat -- New feature
• fix -- Bug fix
• docs -- Documentation only
• chore -- Maintenance task (deps, config, etc.)
• refactor -- Code restructuring (no behavior change)
• test -- Adding or updating tests
• ci -- CI/CD pipeline changes
• build -- Build system or dependency changes
• revert -- Reverts a previous commit
• style -- Code style (formatting, whitespace)

Modifiers

• Breaking change (!) -- This change breaks backward compatibility

Changes Made

• Updated .devcontainer/docker-compose.yml
• Replaced ghcr.io/vig-os/devcontainer:dev
• With ghcr.io/vig-os/devcontainer:0.2.1
• No other configuration changes were made

Changelog Entry

No changelog needed — this is an internal configuration maintenance change and does not affect end users.

Testing

• Tests pass locally (just test)
• Manual testing performed (describe below)

Manual Testing Details

• Verified only the image tag changed using git diff
• Confirmed no additional configuration modifications were introduced

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly (edit docs/templates/, then run just docs)
• I have updated CHANGELOG.md in the [Unreleased] section (and pasted the entry above)
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Additional Notes

This change improves environment stability by avoiding the use of a moving development tag.

Refs: #6