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>

LOTUS_TODO.md

@@ -35,7 +35,9 @@ Completed features are documented in [LOTUS_FEATURES.md](./LOTUS_FEATURES.md).
 
 ## 🔎 Audit findings — Wave 1 (2026-07)
 
-Bug-hunt of the Tier-1 high-risk areas (notifications/unread/receipts, threads, calls host-side, Element Call fork) by 4 parallel deep-audit agents. **Findings only — not yet fixed.** Fix in prioritized, individually-tested passes (each 🔴 first). `[T#]`=threads, `[N#]`=notifications, `[C#]`=calls host, `[EC#]`=fork. Top-two 🔴 hand-verified against the code.
+Bug-hunt of the Tier-1 high-risk areas (notifications/unread/receipts, threads, calls host-side, Element Call fork) by 4 parallel deep-audit agents. `[T#]`=threads, `[N#]`=notifications, `[C#]`=calls host, `[EC#]`=fork.
+
+**✅ FIXED (2026-07):** all 🔴 (T1, N1, N2) + web 🟠 (T2, T4, N3, N4). Web fixes are gate-green (678 tests incl. the new `threadReceipt.test.ts` locking the T1 regression). EC-fork 🟡 (EC1–EC6) fixed on `element-call:lotus` (needs a republish). **Still open:** calls-host 🟠/🟡 (C-H1/2/3, C-M*, C-L*) — see below; the remaining 🟡 notification/thread tail (N5, N6, T5, T6, T7).
 
 ### 🔴 High — data-integrity / broken core UX