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/sheet-dismiss.test.ts

@@ -0,0 +1,52 @@
+import "@testing-library/jest-dom/vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+import { sheetDismiss } from "../src/lib/ui/sheet-dismiss";
+
+// Only the tap-outside path is unit-tested; the swipe-down drag is
+// pointer-gesture behaviour covered by manual / e2e checks.
+describe("sheetDismiss — tap outside", () => {
+	let cleanup: (() => void) | null = null;
+
+	afterEach(() => {
+		cleanup?.();
+		cleanup = null;
+		document.body.innerHTML = "";
+	});
+
+	it("dismisses on a pointer-down outside the sheet", () => {
+		const node = document.createElement("div");
+		const outside = document.createElement("button");
+		document.body.append(node, outside);
+		const onDismiss = vi.fn();
+		const action = sheetDismiss(node, { onDismiss });
+		cleanup = action.destroy;
+
+		outside.dispatchEvent(new MouseEvent("pointerdown", { bubbles: true }));
+		expect(onDismiss).toHaveBeenCalledOnce();
+	});
+
+	it("ignores a pointer-down inside the sheet", () => {
+		const node = document.createElement("div");
+		const inner = document.createElement("button");
+		node.append(inner);
+		document.body.append(node);
+		const onDismiss = vi.fn();
+		const action = sheetDismiss(node, { onDismiss });
+		cleanup = action.destroy;
+
+		inner.dispatchEvent(new MouseEvent("pointerdown", { bubbles: true }));
+		expect(onDismiss).not.toHaveBeenCalled();
+	});
+
+	it("stops listening after destroy", () => {
+		const node = document.createElement("div");
+		const outside = document.createElement("button");
+		document.body.append(node, outside);
+		const onDismiss = vi.fn();
+		sheetDismiss(node, { onDismiss }).destroy();
+
+		outside.dispatchEvent(new MouseEvent("pointerdown", { bubbles: true }));
+		expect(onDismiss).not.toHaveBeenCalled();
+	});
+});