Phase 6: polish — error boundaries, a11y, smoke test doc

Close out the read-only surface before cutover with three families of
small fixes that the previous phases left unfinished:

- Error boundaries: add src/app/error.tsx (route-segment), global-error.tsx
  (root crash fallback with its own minimal html/body — no Providers
  dependency since those may be the thing that crashed), and not-found.tsx
  for a Hebrew 404 instead of the default Next page.

- Accessibility: wire usePathname() into AppShell so the current nav item
  gets aria-current="page" and a gold underline. Add aria-label + aria-hidden
  on the icon-only buttons that Phase 5 left text-less (corpus trash,
  parties-field Plus). Nav gets an aria-label of its own.

- Metadata template: title on each route now reads "X · עוזר משפטי" via
  the layout.tsx title.template. Description localized to Jerusalem.

- README: full E2E smoke test checklist covering all 9 screens, plus a
  backend contract table so future phases know which hook wraps which
  endpoint. Documents the known Gitea→Coolify webhook issue.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web-ui/src/app/error.tsx

@@ -0,0 +1,57 @@
+"use client";
+
+import { useEffect } from "react";
+import Link from "next/link";
+import { AlertTriangle } from "lucide-react";
+import { Button } from "@/components/ui/button";
+
+/*
+ * Route-segment error boundary. Next 16 App Router convention: this file
+ * catches render-time errors thrown below the root layout. `reset` clears
+ * the error and re-renders the segment; we keep the user's nav in place
+ * (no AppShell here — the shell re-renders from the layout above us).
+ */
+export default function ErrorPage({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  useEffect(() => {
+    console.error("Route error:", error);
+  }, [error]);
+
+  return (
+    <main className="flex-1 w-full max-w-[1400px] mx-auto px-10 py-10">
+      <div className="max-w-xl mx-auto text-center space-y-5 py-16">
+        <AlertTriangle className="w-12 h-12 text-danger mx-auto" aria-hidden="true" />
+        <div className="space-y-2">
+          <h1 className="text-navy">משהו השתבש</h1>
+          <p className="text-ink-muted leading-relaxed">
+            נכשלה טעינת המסך. זה עשוי להיות כשל זמני ברשת או באחד מה-endpoints
+            של FastAPI.
+          </p>
+          {error.digest && (
+            <p className="text-[0.72rem] text-ink-light tabular-nums">
+              error id: {error.digest}
+            </p>
+          )}
+          {error.message && (
+            <code className="text-[0.78rem] text-ink-soft bg-rule-soft/60 rounded px-3 py-1 inline-block mt-2">
+              {error.message}
+            </code>
+          )}
+        </div>
+        <div className="flex items-center justify-center gap-3">
+          <Button onClick={reset} className="bg-navy hover:bg-navy-soft text-parchment">
+            נסה שוב
+          </Button>
+          <Button variant="outline" asChild>
+            <Link href="/">חזרה לבית</Link>
+          </Button>
+        </div>
+      </div>
+    </main>
+  );
+}