feat(ui): error & state UX — error surface, view states, map selection, sheet gestures (F4)

- lib/error/: classify any caught error into a stable ErrorKind from the
  transport signal (HTTP status / Connect Code / fetch TypeError /
  navigator.onLine); map to translated error.* messages via reportError
  (sticky Retry toast for retryable kinds) or errorMessageKey (inline).
  Mail compose now surfaces the translated 403/error inline.
- lib/ui/view-state.svelte: shared loading/empty/error placeholder with
  the right live-region role + optional action; entity tables
  (races/sciences/ship-classes) migrated, rest adopt incrementally.
- map/selection-ring.ts: accent ring around the selected planet, fed into
  the map buildExtras alongside the reach circles.
- lib/ui/sheet-dismiss.ts: tap-outside + drag-handle swipe-down dismissal
  for the planet/ship-group bottom-sheets (hand-rolled pointer events).

Tests: error, view-state, selection-ring, sheet-dismiss (761 total).
Docs: ui/docs/error-state-ux.md (+ index); F4 marked done.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/docs/README.md

@@ -15,6 +15,9 @@ lives in [`../PLAN.md`](../PLAN.md), the active web finalization in
 - [a11y.md](a11y.md) — the WCAG 2.2 AA approach: axe + keyboard test
   gates, the shared a11y primitives, coverage by area, and the map-canvas
   alternative.
+- [error-state-ux.md](error-state-ux.md) — the central error surface
+  (taxonomy → translated/actionable messages), the shared `ViewState`
+  placeholder, the selected-planet ring, and bottom-sheet dismissal.
 - [navigation.md](navigation.md) — routes, the sidebar tabs, and the
   state-preservation rules across view/tab switches.
 - [storage.md](storage.md) — the `KeyStore` and `Cache` abstractions and