[Colorful List] Preserve article background on hover

[JamBalaya56562]

Summary

• move the generated feed color from an inline background declaration to a CSS custom property
• apply that color consistently to the article header and title while hovering
• register the extension stylesheet and bump Colorful List to 0.3.3

Fixes #203

Root cause

Colorful List set the article header background through an inline shorthand declaration. FreshRSS themes change both the header and title backgrounds on hover, but the inline header background won the cascade while the title received the theme hover color. This produced two different backgrounds within the same row.

Visual comparison

The screenshots use the same FreshRSS feed, Origine light theme, 1280×720 viewport, and first article. Because the available browser runner cannot activate the CSS :hover pseudo-class, a test-only stylesheet replaced :hover with a class for the first row. The stylesheet used the exact Origine hover declarations and was served only by the local test proxy; it is not part of this PR.

Before

The title area uses the theme hover color while the rest of the row retains the generated feed color.

After

The title, header, and date area retain one continuous generated feed color.

Computed colors for the simulated hovered first row:

• Before: header rgba(139, 178, 195, 0.07); title rgb(250, 238, 232)
• After: header and title rgba(139, 178, 195, 0.07)

Validation

• npm run eslint
• npx stylelint "**/*.css"
• npm run markdownlint
• verified initial entries and dynamically loaded entries continue receiving the CSS custom property through the existing observer
• verified the normal and simulated-hover states in FreshRSS 1.29.2-dev with Colorful List enabled

[Frenzie]

Pinging @shinemoon