feat: frictionless custom domain management

- Edit domains inline (pencil icon, saves on Enter)
- Suggested domains: clickable chips for popular AI/dev/collab sites
- Bulk add: paste multiple domains at once (one per line or comma-separated)
- Popup domain management: add/remove/suggestions directly from the popup
- Permission revoke on removal + suggested list updates dynamically

https://claude.ai/code/session_01KF4i7Ra7zCEDskxDBaNtcT

src/popup/popup.html

@@ -236,6 +236,19 @@
         <label class="toggle"><input type="checkbox" id="optDocPreview" checked><span class="toggle-slider"></span></label>
       </div>
 
+      <div style="margin-top:12px;padding-top:10px;border-top:1px solid #e5e7eb">
+        <div class="setting-label" style="margin-bottom:6px">
+          <strong>Custom Domains</strong>
+          <span class="setting-desc">Add sites beyond the built-in list</span>
+        </div>
+        <div id="popupDomainList" style="max-height:120px;overflow-y:auto;margin-bottom:6px"></div>
+        <div style="display:flex;gap:4px">
+          <input type="text" id="popupNewDomain" placeholder="https://ai.example.com" style="flex:1;font-size:11px;padding:4px 6px;border:1px solid #d1d5db;border-radius:4px;min-width:0">
+          <button class="btn" id="btnPopupAddDomain" style="font-size:11px;padding:4px 8px;white-space:nowrap">Add</button>
+        </div>
+        <div id="popupDomainSuggestions" style="margin-top:6px;display:flex;flex-wrap:wrap;gap:3px"></div>
+      </div>
+
       <div style="margin-top:12px;padding-top:10px;border-top:1px solid #e5e7eb">
         <button class="btn" id="btnOpenFullOptions" style="width:100%;font-size:12px">Open Full Options Page</button>
         <p class="help-text" style="margin-top:6px;text-align:center">Sync, encryption, org, version history, import/export, and more</p>