Use explicit .post-description class for blog listing description (closes #296)

[twill-hq]

Task created from Twill by Paul Keen.

Summary

Replaces the fragile positional selector .post-content > div:last-child with an explicit .post-description class on the blog post listing description. Closes #296.

The positional selector breaks silently if the post card markup grows another trailing element. An explicit class survives template restructuring.

Changes

• themes/beaver/layouts/blog/list.html — added class="post-description" to the <div> rendering .Params.description.
• themes/beaver/assets/css/homepage-layout.css — replaced selector in both the main rule and the @media (max-width: 860px) rule. Rule body is identical (font-size: 0.85em, line-height: 1.5, color: #555, margin-top: 6px).

Verification

• bin/hugo-build passed (Hugo 0.161.1, matches CI).
• 10 .post-description elements render on /blog/ index.
• Computed styles on the rendered description match pre-change values:
  • font-size: 15.3px (= 0.85em)
  • line-height: 22.95px (= 1.5)
  • color: rgb(85, 85, 85) (= #555)
  • margin-top: 6px
• Mobile (window.innerWidth = 375): display: none — media query still hides description.
• rg confirms no other rule depended on .post-content > div:last-child and no other consumer references it.

Visual evidence

Desktop (1280px) — descriptions visible:

Mobile (375px) — descriptions hidden by media query, matching pre-change behavior:

Note on test gates

The CLAUDE.md visual regression gate normally runs bin/test and bin/dtest. Those Ruby/Docker harnesses are not available in this sandbox, so this PR substitutes:

1. A clean Hugo build matching CI's Hugo version.
2. Direct DOM and computed-style assertions on the rendered output (above).
3. Desktop + mobile screenshots showing identical visual output.

CSS specificity does increase from (0,0,2) to (0,1,0), but the rule sits in a self-contained block with no competing selectors targeting .post-description, so behavior is preserved.

Test plan

• CI build (_hugo.yml) passes
• Verify /blog/ description rendering on the Preview (desktop + < 860px viewport)
• Maintainer runs bin/test and bin/dtest locally if visual baseline parity is required

View on Twill

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