fix: customer search & linking fully implemented

- Add ajax_search_wc_customers() – searches user_login, user_email,
  display_name AND first_name/last_name meta so any query returns hits
- Add ajax_unlink_customer() to remove an existing Odoo link
- Replace placeholder Customers tab with two-panel UI:
  Step 1 search WC customers → Step 2 search Odoo partners independently
  (WC email and Odoo email do not need to match)
- Results table shows current link status; inline Link/Unlink actions
  update the row in-place without page reload
- Admin JS fully wired: both search inputs respond to Enter key and button
- Add two-panel layout CSS and results table styles

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

assets/css/woodoo-admin.css

@@ -24,3 +24,47 @@
 }
 .woodoo-badge--green { background: #d1fae5; color: #065f46; }
 .woodoo-badge--red   { background: #fee2e2; color: #991b1b; }
+.woodoo-badge--grey  { background: #f3f4f6; color: #6b7280; }
+
+/* ── Two-panel customer linker ────────────────────────────────────────── */
+.woodoo-linker-panel {
+    display: flex;
+    gap: 24px;
+    align-items: flex-start;
+    margin-top: 12px;
+}
+.woodoo-linker-col {
+    flex: 1;
+    min-width: 0;
+    background: #f9fafb;
+    border: 1px solid #e5e7eb;
+    border-radius: 6px;
+    padding: 16px;
+}
+.woodoo-linker-col h3 {
+    margin: 0 0 10px;
+    font-size: 1rem;
+    color: #2271b1;
+}
+.woodoo-search-row {
+    display: flex;
+    gap: 6px;
+    margin-bottom: 12px;
+}
+.woodoo-search-row .regular-text { flex: 1; margin: 0; }
+.woodoo-results-list { margin-top: 4px; }
+.woodoo-no-results { color: #6b7280; font-style: italic; margin: 8px 0 0; }
+.woodoo-linking-for {
+    font-size: .875rem;
+    background: #eff6ff;
+    border: 1px solid #bfdbfe;
+    border-radius: 4px;
+    padding: 6px 10px;
+    margin: 0 0 10px;
+}
+
+/* ── Results table ────────────────────────────────────────────────────── */
+.woodoo-link-table { font-size: .8125rem; }
+.woodoo-link-table th { padding: 6px 8px; font-weight: 600; background: #f3f4f6; }
+.woodoo-link-table td { padding: 6px 8px; vertical-align: middle; }
+.woodoo-link-table tr:hover td { background: #fafafa; }