feat: disable until configured + auto permission request for custom domains

Interception is now completely inactive until the user configures
at least one identity field or explicit mapping. Before that:
- Icon shows gray (unconfigured)
- No fetch/XHR hooks fire
- First-run banner tells user to set up

Custom domains: clicking "Add Domain" in Options now triggers
the browser's native permission prompt via permissions.request().
No more manual chrome://extensions site access step.

Icon states are now:
- Gray = unconfigured (nothing will happen)
- Black = active and protecting
- Blue = reveal mode on
- Red = manually disabled

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/content/content.js

@@ -446,12 +446,20 @@
   // ============================================================
   // Check if we have anything to substitute
   // ============================================================
-  function hasSubstitutions() {
+  // Check if the user has configured anything at all.
+  // If not, the extension is effectively disabled — no interception.
+  function isConfigured() {
     return mappings.length > 0 ||
       (identity.emails || []).length > 0 ||
       (identity.names || []).length > 0 ||
       (identity.usernames || []).length > 0 ||
-      (identity.phones || []).length > 0;
+      (identity.hostnames || []).length > 0 ||
+      (identity.phones || []).length > 0 ||
+      !!identity.catchAllEmail;
+  }
+
+  function hasSubstitutions() {
+    return isConfigured();
   }
 
   // ============================================================