fix(notifications/threads): Wave-1 audit fixes (🔴 + web 🟠)

- T1 (🔴): markThreadAsRead no longer receipts the thread ROOT (a 2nd instance
  of the read-marker-corruption regression — opening a thread whose root is old
  re-lit the whole room). Extracted to a pure threadReceipt.ts + 5 regression
  tests.
- N1 (🔴): favicon/tab-title unread count now sums only leaf rooms (was double-
  counting every ancestor-space aggregate in roomToUnread).
- N2 (🔴): notifications/sounds dedupe on the event id, not the unread count —
  fixes "read a DM, next message never notifies again".
- T4 (🟠): the thread notification path no longer re-gates on the room count, so
  an explicit per-thread "All replies" override in a Mentions-only room fires.
- N3 (🟠): getUnreadInfos skips phantom {0,0} entries (muted-thread-only rooms no
  longer light the nav row / pollute unread filters).
- N4 (🟠): the Receipt handler recomputes unread instead of blanket-DELETE, so a
  threaded receipt can't wipe a room's valid main-timeline badge.
- T2 (🟠): thread "Jump to Latest" re-anchors the virtual window (was landing on
  a stale mid/old event).

Gates: tsc/eslint/prettier clean, build OK, 678 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/utils/room.ts

@@ -269,7 +269,15 @@ export const getUnreadInfos = (
 
     if (roomHaveNotification(room) || roomHaveUnread(mx, room)) {
       const mutedThreads = content ? getMutedThreads(content, room.roomId) : undefined;
-      unread.push(getUnreadInfo(room, mutedThreads));
+      const info = getUnreadInfo(room, mutedThreads);
+      // Skip a phantom {0,0} entry: a room whose ONLY unread is a muted thread has
+      // roomHaveNotification true (the server room total includes the muted
+      // thread's count), but getUnreadInfo subtracts it back to zero. Pushing it
+      // would still light the nav row + pollute "unread only" filters. Keep it
+      // only if there's real unread (count > 0) or a genuine unread marker.
+      if (info.total > 0 || info.highlight > 0 || roomHaveUnread(mx, room)) {
+        unread.push(info);
+      }
     }
 
     return unread;