Banner SVG fixes

[wallstop]

Description

Banner SVG updates and styling to render more uniformly across devices

Related Issue

Fixes #172
Fixes #171

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactor (code change that neither fixes a bug nor adds a feature)

Checklist

• I have added tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have updated the CHANGELOG
• My changes do not introduce breaking changes, or breaking changes are documented

[Copilot]

Pull request overview

Updates the Unity Helpers banner SVG and related styling so it renders more consistently across devices/backgrounds, and adds a devcontainer fix to avoid apt failures from an expired Yarn repo key.

Changes:

• Adjusted the banner SVG (transparent outer background, added backdrop, tweaked filters/letter-spacing for improved readability/kerning).
• Added CSS rules to center/scale the banner consistently in MkDocs pages.
• Updated CHANGELOG.md and patched the devcontainer to remove an expired Yarn apt source.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

File	Description
docs/stylesheets/custom.css	Adds .md-banner layout rules to center and scale the banner on docs pages.
docs/images/unity-helpers-banner.svg	Updates SVG rendering (background/backdrop, filters, spacing) to improve appearance across devices/themes.
CHANGELOG.md	Notes the banner SVG rendering fixes under Unreleased.
.devcontainer/Dockerfile	Removes Yarn apt source/key to prevent apt-get update failures due to an expired GPG key.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 7 changed files in this pull request and generated no new comments.