Convert im_webapp from static mock prototypes to real backend integration

Implements all 11 product chapters (auth, messaging, contacts, groups,
files/favorites, calls, workplace/reports, settings, security) against the
real /v1/im REST API and native Tinode WS protocol, replacing the hardcoded
mock data the ba8f48ee prototype commit shipped with. Adds src/lib/im-api.js
as the REST client, plus supporting fixes across messages-view.jsx and the
attachment/upload/download pipeline (wrong SDK auth headers, group topic
naming, seq/timezone edge cases) found via live end-to-end testing against
the real backend.

Backup checkpoint before reconciling with origin/dev's parallel rewrite.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/widgets/contact-list.jsx

@@ -9,6 +9,7 @@ import Contact from './contact.jsx';
 import ContactAction from './contact-action.jsx';
 
 import { makeImageUrl } from '../lib/blob-helpers.js';
+import { topicDisplayName } from '../lib/utils.js';
 
 import { MESSAGE_PREVIEW_LENGTH } from '../config.js';
 
@@ -35,8 +36,8 @@ class ContactList extends React.PureComponent {
     let contactsCount = 0;
     if (this.props.showSelfTopic) {
       const selected = showCheckmark ?
-        (this.props.topicSelected.indexOf('slf') > -1) :
-        (this.props.topicSelected === 'slf');
+        this.props.topicSelected.some(Tinode.isSelfTopicName) :
+        Tinode.isSelfTopicName(this.props.topicSelected);
       contactNodes.push(
         <Contact
           tinode={this.props.tinode}
@@ -78,8 +79,9 @@ class ContactList extends React.PureComponent {
             if (c.private && c.private.comment) {
               filterOn.push(('' + c.private.comment).toLowerCase());
             }
-            if (c.public && c.public.fn) {
-              filterOn.push(('' + c.public.fn).toLowerCase());
+            const displayName = topicDisplayName(key, c.public, null);
+            if (displayName) {
+              filterOn.push(('' + displayName).toLowerCase());
             }
             if (!this.props.filterFunc(this.props.filter, filterOn)) {
               return;
@@ -124,7 +126,7 @@ class ContactList extends React.PureComponent {
           contactNodes.push(
             <Contact
               tinode={this.props.tinode}
-              title={c.public ? c.public.fn : null}
+              title={c.public ? topicDisplayName(key, c.public, null) : null}
               avatar={makeImageUrl(c.public ? c.public.photo : null)}
               comment={comment}
               preview={preview}