Fix Paperclip integration (identifier→issue_prefix) + add settings page

- Fix column name mismatch in paperclip_client.py and app.py: Paperclip's
  companies table uses `issue_prefix`, not `identifier`
- Fix _LEGAL_DB_URL to read from POSTGRES_URL env var (used in container)
- Add settings page (/settings) for managing tag → Paperclip company mappings
- Replace "תיק חדש" nav item with "הגדרות" (new case is on home page)

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

web-ui/src/lib/api/settings.ts

@@ -0,0 +1,57 @@
+/**
+ * Settings hooks: tag → Paperclip company mappings.
+ */
+
+import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query";
+import { apiRequest } from "./client";
+
+export type PaperclipCompany = {
+  id: string;
+  name: string;
+  prefix: string;
+};
+
+export type TagMapping = {
+  id: string;
+  tag: string;
+  tag_label: string;
+  company_id: string;
+  company_name: string;
+  created_at: string;
+};
+
+export function usePaperclipCompanies() {
+  return useQuery({
+    queryKey: ["settings", "paperclip-companies"] as const,
+    queryFn: ({ signal }) =>
+      apiRequest<PaperclipCompany[]>("/api/settings/paperclip-companies", { signal }),
+    staleTime: 60_000,
+  });
+}
+
+export function useTagMappings() {
+  return useQuery({
+    queryKey: ["settings", "tag-mappings"] as const,
+    queryFn: ({ signal }) =>
+      apiRequest<TagMapping[]>("/api/settings/tag-mappings", { signal }),
+    staleTime: 10_000,
+  });
+}
+
+export function useAddTagMapping() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (body: { tag: string; tag_label: string; company_id: string; company_name: string }) =>
+      apiRequest<TagMapping>("/api/settings/tag-mappings", { method: "POST", body }),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["settings", "tag-mappings"] }),
+  });
+}
+
+export function useDeleteTagMapping() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (id: string) =>
+      apiRequest<{ ok: boolean }>(`/api/settings/tag-mappings/${id}`, { method: "DELETE" }),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["settings", "tag-mappings"] }),
+  });
+}