refactor(decnet_web/AttackerDetail): extract AttackerHeader section

Lift the header (IP, country tag, traversal badge, identity badge)
into its own section component. Tag helper moves to a shared
AttackerDetail/ui.tsx so future sections can reuse it without
re-importing through AttackerDetail.tsx.

- New AttackerDetail/sections/AttackerHeader.tsx (~50 LOC)
- New AttackerDetail/ui.tsx for shared presentational helpers
- AttackerDetail.tsx imports both; local Tag definition deleted
- AttackerHeader.test.tsx covers country present/absent,
  TRAVERSAL badge, IDENTITY click-through, identity null path

decnet_web/src/components/AttackerDetail/sections/AttackerHeader.tsx

@@ -0,0 +1,50 @@
+import React from 'react';
+import { useNavigate } from 'react-router-dom';
+import { Crosshair } from '../../../icons';
+import { Tag } from '../ui';
+import type { AttackerData } from '../types';
+
+interface Props {
+  attacker: AttackerData;
+}
+
+/** Page header: crosshair + IP + country / traversal / identity badges.
+ *  The identity badge is click-through to the resolved-actor page. */
+export const AttackerHeader: React.FC<Props> = ({ attacker }) => {
+  const navigate = useNavigate();
+  return (
+    <div style={{ display: 'flex', alignItems: 'center', gap: '16px' }}>
+      <Crosshair size={32} className="violet-accent" />
+      <h1 className="matrix-text" style={{ fontSize: '1.8rem', letterSpacing: '2px' }}>
+        {attacker.ip}
+      </h1>
+      {attacker.country_code && (
+        <Tag color="var(--text-color)">
+          <span
+            title={attacker.country_source ? `source: ${attacker.country_source}` : undefined}
+            style={{ letterSpacing: '2px' }}
+          >
+            {attacker.country_code}
+          </span>
+        </Tag>
+      )}
+      {attacker.is_traversal && (
+        <span className="traversal-badge" style={{ fontSize: '0.8rem' }}>TRAVERSAL</span>
+      )}
+      {attacker.identity_id && (
+        <span
+          className="traversal-badge"
+          style={{
+            fontSize: '0.8rem',
+            cursor: 'pointer',
+            letterSpacing: '2px',
+          }}
+          title="Resolved identity — click to view all observations linked to this actor"
+          onClick={() => navigate(`/identities/${attacker.identity_id}`)}
+        >
+          IDENTITY · {attacker.identity_id.slice(0, 8)}
+        </span>
+      )}
+    </div>
+  );
+};