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/frontend/tests/selection-ring.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, it } from "vitest";
+
+import {
+	computeSelectionRing,
+	SELECTION_RING_COLOR,
+	SELECTION_RING_ID,
+} from "../src/map/selection-ring";
+
+const planets = [
+	{ number: 1, x: 10, y: 20 },
+	{ number: 2, x: 30, y: 40 },
+];
+
+describe("computeSelectionRing", () => {
+	it("returns null when nothing is selected", () => {
+		expect(computeSelectionRing(planets, null)).toBeNull();
+	});
+
+	it("returns null when the selected planet is absent from the report", () => {
+		expect(computeSelectionRing(planets, 99)).toBeNull();
+	});
+
+	it("rings the selected planet at its coordinates", () => {
+		const ring = computeSelectionRing(planets, 2);
+		expect(ring).toMatchObject({
+			kind: "circle",
+			id: SELECTION_RING_ID,
+			x: 30,
+			y: 40,
+			hitSlopPx: 0,
+		});
+		expect(ring?.style.strokeColor).toBe(SELECTION_RING_COLOR);
+		// Sits outside the planet marker (radius 6 world units).
+		expect(ring?.radius ?? 0).toBeGreaterThan(6);
+	});
+});