design(ui): fill civiccore-ui/components/ and shell/ (canonical component + shell layers)

[scottconverse]

Fills the two remaining empty slots in civiccore-ui/ (were .gitkeep-only), completing the design system alongside tokens/.

• components/components.css (352 lines) — buttons, badges, status ribbon, tables, forms, alerts, first-run setup steps, empty states, the hash-chained audit drawer. Extracted faithfully from the canonical umbrella prototype (docs/design/ui-ux-prototype/styles.css) — same class names, same behavior — consuming tokens.css for every value. One AA fix at extraction: .badge.gold uses --gold-strong (5.43:1) instead of --gold-2 (4.31:1, a fail).
• components/components-reference.html — live showcase of every component on the tokens.
• shell/shell.css (446 lines) — the app frame (brand, topbar, surface switcher, nav, workspace, page header, letterhead, search overlay).
• civiccore-ui/README.md — documents the three-layer system, dependency direction, and the vendored-copy + drift-gate consumption rule.

Verified: every var() used is defined in tokens.css (0 undefined tokens); no layer redefines a tokens.css :root property. Consumer migration (prototype + desktop consuming these instead of their own copies) is the incremental follow-on.