Empty states and illustration style: on-brand spot illustrations, one-line value, primary action with shortcut

Part of PAR-357.

Problem

Empty states are where a product sells its next feature, and ours are dead ends:

• Board columns: a bordered box reading "No issues".
• Releases with no GitHub: a grey footnote about develop → main PRs.
• New workspace: a "Welcome to {ws} 👋" checklist of three links.
• Teams with one team: a single bar on an empty page.
• Comments: "No comments yet."
• Generic StateBlocks wherever data is missing.

None of them use illustration, explain why you'd want the thing, or offer a primary action with its shortcut. The landing site has a recognisable visual motif (the terracotta asterisk, sage checkmark squircle and editorial type) that the app never reuses.

Reference

• Linear Projects empty state: an isometric line illustration, a short explanation of what projects are for, "Create new project N then P" and "Documentation" (Mobbin).
• Productboard: an illustration plus a "Create" menu offering types (Mobbin).
• Figma: a colourful brand-motif illustration (Mobbin).

Do

• Define an illustration style from the landing's motifs: line art in sage with terracotta accents, built on the icon stroke weight, and good in both themes.
• Build an EmptyState component (illustration · title · one sentence of value · primary action with Kbd · optional secondary "Learn more") and use it on:
  • Issues (none / filtered to none, with "Clear filters")
  • Board column (compact: "+ Add issue")
  • Projects, Releases ("Connect GitHub to create releases automatically")
  • Inbox ("You're all caught up")
  • My issues, Search (no results), Comments ("Start the discussion"), Analytics (not enough data)
• Use a tiny celebratory moment for Inbox zero and for completing the onboarding checklist, respecting reduced motion.
• Remove emoji from UI copy in favour of the illustration system.