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/components/app-shell.tsx

@@ -24,10 +24,10 @@ type NavItem = {
 
 const NAV_ITEMS: NavItem[] = [
   { href: "/",            label: "בית"         },
-  { href: "/cases/new",   label: "תיק חדש"     },
   { href: "/training",    label: "אימון סגנון" },
   { href: "/skills",      label: "מיומנויות"  },
   { href: "/diagnostics", label: "אבחון"       },
+  { href: "/settings",    label: "הגדרות"      },
 ];
 
 function isActive(pathname: string, href: string): boolean {