Add the "Latest activity" strip to the home page #279

Part of #271 (Phase 4).

Why. Option c1, decided in #266: a compact "Latest activity" strip under the home page's three news cards shows at a glance that the project is active. The design is section 3 of the round-2 handoff, amended by the round-2 decision (see the round 2 outcome).

The problem the amendment fixes. As handed off, each item's type label (a translation's language, "3 editions", "4 releases · same day") is truncated along with the title. Long series names are cut hard: in the prototype, "Intermediate Quantitative Economics with Python" showed 25 of its 47 characters at 1200–1399px, and "Intermediate …" at 768–991px.

Work.

• At 1200px and wider, one compact line:
  • the type label sits outside the truncated title, so it's never cut;
  • items are sized to their content, so short titles give their space to long ones;
  • the link reads "View all activity →".
• Below 1200px, the stacked list: 44px rows, with the icons kept.
• Merged rows link to their day on /activity/ (#activity-YYYY-MM-DD), which Restyle /activity/ with the shared rows, a type filter and day links #277 adds.
• Card dates change to "Jul 14, 2026" (%b %-d, %Y). Their #666 colour already landed in Fix tag-pill contrast and make the news-card focus ring visible #269.

Acceptance criteria

• Handoff check 5: the strip shows the three newest rows (today: Sep 27 Intermediate Quantitative Economics with Python, Sep 24 QuantEcon.py v0.12.0, Sep 23 GameTheory.jl v0.7.2).
• At 1200, 1280 and 1440px, a translation's language and a group's label are never cut. Check with a placeholder built from the Aug 3 and Aug 2 rows.
• Below 1200px the stacked list shows, with no horizontal scroll at 320px.
• AA contrast and visible focus on every item.