feat(woo): S4 Woo client + taxonomy sync + test-woo + admin taxonomy

- backend/woo.py: stdlib urllib Woo v3 client. Basic-auth, HTTPS-only, X-WP-TotalPages
  pagination, typed errors (CredentialsMissing/Auth/NotFound/Server/Connection),
  injectable transport for tests, WP core media upload.
- backend/taxonomy.py: sync pulls categories/tags/attributes/terms into cache in one
  commit (rollback keeps prior cache on failure); fig-*/feat-* tag scoping; stable
  taxonomy_anchor hash; get_cached grouped admin view.
- backend/app.py: POST /settings/test-woo (fail-closed, resync on success),
  GET /admin/taxonomy, POST /admin/taxonomy/sync (502 on Woo failure).
- frontend: Settings Test Woo button + result display.
- tests: 8 woo/taxonomy tests (auth header, non-https refusal, pagination, missing
  creds, 401, scoped sync, failure-keeps-cache, anchor stability).

Verified: pytest 31 passed; check_requirements + check_coverage exit 0; npm build ok;
live QA test-woo fail-closed + sync 502.

frontend/src/create/settings/Settings.svelte

@@ -91,6 +91,18 @@
     saving = false;
   }
 
+  let testResult: { ok: boolean; detail: string } | null = null;
+
+  async function testWoo() {
+    testResult = null;
+    try {
+      const res = await fetch('/api/v1/settings/test-woo', { method: 'POST' });
+      testResult = await res.json();
+    } catch {
+      testResult = { ok: false, detail: 'network error' };
+    }
+  }
+
   onMount(() => {
     void load();
   });
@@ -158,6 +170,12 @@
     </div>
 
     <button on:click={save} disabled={saving}>Save Changes</button>
+    <button on:click={testWoo} disabled={saving}>Test Woo</button>
+    {#if testResult}
+      <p class="msg" class:ok={testResult.ok} class:err={!testResult.ok}>
+        {testResult.ok ? 'Connected & synced' : testResult.detail}
+      </p>
+    {/if}
     {#if message}<p class="msg">{message}</p>{/if}
   {/if}
 </div>