feat(forward): Discord-style provenance — 'Forwarded from <sender> in <room> · <time>' with jump to the original

Forwarded events carried no origin at all; they read as the forwarder's own
words. buildForwardContent now stamps io.lotus.forwarded (sender, ts,
room_id, event_id; re-forwards keep the original stamp) and the main and
thread timelines render a reply-style header above the message that jumps
to the original when the viewer is in the source room (sender + time only
otherwise — the source room's name is not leaked). Unit-tested; verified
end to end with Playwright (header text, event content, jump, re-forward).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/room/thread/ThreadTimeline.tsx

@@ -38,10 +38,13 @@ import { useMatrixClient } from '../../../hooks/useMatrixClient';
 import { useVirtualPaginator, ItemRange } from '../../../hooks/useVirtualPaginator';
 import { useAlive } from '../../../hooks/useAlive';
 import { editableActiveElement, scrollToBottom } from '../../../utils/dom';
+import { getForwardedMeta } from '../message/forwardContent';
+import { useRoomNavigate } from '../../../hooks/useRoomNavigate';
 import {
   DefaultPlaceholder,
   MessageBase,
   Reply,
+  ForwardedHeader,
   RedactedContent,
   MSticker,
   MessageUnsupportedContent,
@@ -267,6 +270,7 @@ export function ThreadTimeline({ room, thread, editor }: ThreadTimelineProps) {
   const [encUrlPreview] = useSetting(settingsAtom, 'encUrlPreview');
   const showUrlPreview = room.hasEncryptionStateEvent() ? encUrlPreview : urlPreview;
   const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const { navigateRoom } = useRoomNavigate();
   const [dateFormatString] = useSetting(settingsAtom, 'dateFormatString');
 
   const direct = useIsDirectRoom();
@@ -731,6 +735,7 @@ export function ThreadTimeline({ room, thread, editor }: ThreadTimelineProps) {
       const reactions = reactionRelations?.getSortedAnnotationsByKey();
       const hasReactions = !!reactions && reactions.length > 0;
       const { replyEventId, threadRootId } = mEvent;
+      const forwardedMeta = getForwardedMeta(mEvent.getContent());
 
       return (
         <Message
@@ -755,18 +760,29 @@ export function ThreadTimeline({ room, thread, editor }: ThreadTimelineProps) {
           onReactionToggle={handleReactionToggle}
           onEditId={opts.editable ? handleEdit : undefined}
           reply={
-            replyEventId && (
-              <Reply
-                room={room}
-                timelineSet={timelineSet}
-                replyEventId={replyEventId}
-                threadRootId={threadRootId}
-                onClick={handleOpenReply}
-                getMemberPowerTag={getMemberPowerTag}
-                accessibleTagColors={accessiblePowerTagColors}
-                legacyUsernameColor={legacyUsernameColor || direct}
-              />
-            )
+            <>
+              {forwardedMeta && (
+                <ForwardedHeader
+                  mx={mx}
+                  meta={forwardedMeta}
+                  hour24Clock={hour24Clock}
+                  dateFormatString={dateFormatString}
+                  onJump={() => navigateRoom(forwardedMeta.room_id, forwardedMeta.event_id)}
+                />
+              )}
+              {replyEventId && (
+                <Reply
+                  room={room}
+                  timelineSet={timelineSet}
+                  replyEventId={replyEventId}
+                  threadRootId={threadRootId}
+                  onClick={handleOpenReply}
+                  getMemberPowerTag={getMemberPowerTag}
+                  accessibleTagColors={accessiblePowerTagColors}
+                  legacyUsernameColor={legacyUsernameColor || direct}
+                />
+              )}
+            </>
           }
           reactions={
             reactionRelations && (
@@ -794,6 +810,7 @@ export function ThreadTimeline({ room, thread, editor }: ThreadTimelineProps) {
       );
     },
     [
+      navigateRoom,
       room,
       messageSpacing,
       messageLayout,