feat: normalize remote asset URLs and route UI actions by instance origin

Phase 5 of multi-instance federation. Adds a two-layer fix:

Layer 1 — Data ingestion normalization: Remote instance user avatars,
server icons, and attachment filenames are rewritten to absolute URLs
when entering the app (via WebSocket events or API responses), so all
downstream components render them correctly without changes.

Layer 2 — Outbound action routing: wsSend calls (voice join/leave/status,
typing) and file uploads in UI components now route through the correct
instance based on the active channel's origin.

packages/web/src/components/chat/Message.tsx

@@ -268,14 +268,15 @@ export function Message({ message, isCompact, isFirstInGroup }: MessageProps) {
               <div className="mt-1 grid gap-2">
                 {message.attachments.map((att) => {
                   const isImage = att.mimetype.startsWith('image/');
+                  const attUrl = att.filename.startsWith('http') ? att.filename : `/api/uploads/${att.filename}`;
                   if (isImage) {
                     return (
                       <div key={att.id} className="max-w-fit mt-1 rounded-lg overflow-hidden border border-white/[0.06]">
                         <img
-                          src={`/api/uploads/${att.filename}`}
+                          src={attUrl}
                           alt={att.originalName}
                           className="max-w-full max-h-[350px] object-contain cursor-pointer hover:brightness-95 transition-all"
-                          onClick={() => openImagePreview(`/api/uploads/${att.filename}`)}
+                          onClick={() => openImagePreview(attUrl)}
                           loading="lazy"
                         />
                       </div>
@@ -284,7 +285,7 @@ export function Message({ message, isCompact, isFirstInGroup }: MessageProps) {
                   return (
                     <a
                       key={att.id}
-                      href={`/api/uploads/${att.filename}`}
+                      href={attUrl}
                       download={att.originalName}
                       className="flex items-center gap-3 p-4 bg-surface-channel/50 rounded-lg border border-border-hard hover:bg-interactive-hover transition-all max-w-[400px] mt-1 group/att"
                     >