Add profile feature, input sanitization, and stronger security checks

Backend:
- app/core/sanitize.py: shared sanitize_str, normalize_email, validate_phone,
  validate_date_of_birth — applied to every user-supplied DB-bound input
- app/schemas/user.py: sanitize full_name, normalize email on UserCreate
- app/models/profile.py: profiles table (position, phone, dob, address, updated_at)
- app/models/user.py: Profile back-ref, is_superuser admin-role comment
- app/schemas/profile.py: ProfileRead/ProfileUpdate with full sanitization
- app/routers/profile.py: GET+PUT /api/profile/me (lazy profile creation)
- app/main.py: register /api/profile router
- alembic migration 676084df61d1: create profiles table

Frontend:
- components/Nav.tsx: shared nav (Dashboard | Profile | Logout)
- pages/ProfilePage.tsx: profile view + inline edit form with error handling
- pages/DashboardPage.tsx: use Nav component
- api/client.ts: ProfileData type, getProfile, updateProfile
- App.tsx: /profile private route

Security:
- scripts/security_check.py: tighter SQL injection patterns (f-string/format/%
  in execute/query/text()), new SANIT category for raw request→DB patterns

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/Nav.tsx

@@ -0,0 +1,16 @@
+import { Link } from "react-router-dom";
+import { useAuth } from "../hooks/useAuth";
+
+export default function Nav() {
+  const { logout } = useAuth();
+
+  return (
+    <nav style={{ display: "flex", gap: 16, padding: "12px 24px", borderBottom: "1px solid #ccc" }}>
+      <Link to="/">Dashboard</Link>
+      <Link to="/profile">Profile</Link>
+      <button onClick={logout} style={{ marginLeft: "auto", cursor: "pointer" }}>
+        Logout
+      </button>
+    </nav>
+  );
+}