fix: DM avatar color and reactions in federation + explore/server discovery

- Fix DM welcome header avatar using home identity for correct gradient color
- Register DM channel IDs in channelOriginMap so federated DM operations
  (reactions, messages, typing) route to the correct instance
- Pass origin when creating DM channels from friends list and WS events
- Add server discovery/explore page with public server listings
- Add server visibility and description fields

packages/web/src/components/layout/ServerSidebar.tsx

@@ -14,7 +14,7 @@ interface SidebarItemProps {
   active: boolean;
   onClick: () => void;
   type?: 'server' | 'dm' | 'action';
-  actionType?: 'add' | 'join';
+  actionType?: 'add' | 'join' | 'explore';
   hasUnread?: boolean;
   dimmed?: boolean;
 }
@@ -89,6 +89,10 @@ function SidebarItem({ id, name, icon, active, onClick, type = 'server', actionT
             <svg width="20" height="20" viewBox="0 0 24 24" fill="currentColor">
               <path d="M12 2C6.48 2 2 6.48 2 12s4.48 10 10 10 10-4.48 10-10S17.52 2 12 2zm5 11h-4v4h-2v-4H7v-2h4V7h2v4h4v2z" />
             </svg>
+          ) : actionType === 'explore' ? (
+            <svg width="20" height="20" viewBox="0 0 24 24" fill="currentColor">
+              <path d="M12 2C6.48 2 2 6.48 2 12s4.48 10 10 10 10-4.48 10-10S17.52 2 12 2zm0 18c-4.41 0-8-3.59-8-8s3.59-8 8-8 8 3.59 8 8-3.59 8-8 8zm-5.5-2.5l7.51-3.49L17.5 6.5 9.99 9.99 6.5 17.5zm5.5-6.6c.61 0 1.1.49 1.1 1.1s-.49 1.1-1.1 1.1-1.1-.49-1.1-1.1.49-1.1 1.1-1.1z" />
+            </svg>
           ) : (
             <svg width="20" height="20" viewBox="0 0 24 24" fill="currentColor">
               <path d="M12 2L4.5 20.29l.71.71L12 18l6.79 3 .71-.71z" />
@@ -116,6 +120,8 @@ export function ServerSidebar() {
   const dmChannels = useServerStore((s) => s.dmChannels);
   const showDms = useUIStore((s) => s.showDms);
   const setShowDms = useUIStore((s) => s.setShowDms);
+  const showExplore = useUIStore((s) => s.showExplore);
+  const setShowExplore = useUIStore((s) => s.setShowExplore);
   const openModal = useUIStore((s) => s.openModal);
   const addToast = useUIStore((s) => s.addToast);
   const unreadChannels = useChatStore((s) => s.unreadChannels);
@@ -175,6 +181,7 @@ export function ServerSidebar() {
     }
     setCurrentServer(serverId);
     setShowDms(false);
+    setShowExplore(false);
     navigate(`/channels/${serverId}`);
   };
 
@@ -184,6 +191,12 @@ export function ServerSidebar() {
     navigate('/channels/@me');
   };
 
+  const handleExploreClick = () => {
+    setShowExplore(true);
+    setCurrentServer(null);
+    navigate('/channels/@me');
+  };
+
   return (
     <nav data-pip-obstacle="left" className="w-[72px] bg-surface-base flex flex-col items-center py-3 overflow-y-auto flex-shrink-0 no-scrollbar select-none md:fixed md:inset-y-0 md:left-0 md:z-[100] md:glass-strip">
       <SidebarItem
@@ -257,6 +270,15 @@ export function ServerSidebar() {
         actionType="join"
       />
 
+      <SidebarItem
+        id="explore"
+        name="Explore Servers"
+        active={showExplore}
+        onClick={handleExploreClick}
+        type="action"
+        actionType="explore"
+      />
+
     </nav>
   );
 }