release: v4.8.20 secure chat tools — completed, fixed and polished

Completes the messaging controls from v4.8.14 and fixes the bug that made them
appear broken for recipients.

Fixed:
- Per-message metadata was silently dropped for recipients. NotificationIntegration
  wrapped onMessage and deliverMessageToUI with 2-arg shims that called the
  originals without the 3rd argument (meta); with notifications enabled, view-once,
  disappearing timers and unsend all failed on the receiving side. Both wrappers
  now forward all arguments. Added tests/notification-meta-forwarding.test.mjs.
- Chat would not open after SAS: composer props were threaded into the wrong
  component (EnhancedConnectionSetup vs EnhancedChatInterface) -> ReferenceError
  nowTick on the verified re-render. Props moved to the chat component.

Changed:
- Code blocks: lightweight dependency-free syntax highlighting via React nodes
  (no innerHTML/remote scripts); code mode expands the input; copy auto-clears
  the clipboard after ~30s.
- View-once: configurable visible-after-open time (5s/15s/30s/1m) via meta.onceTtl.
- Disappearing timer: duration picker (Off/30s/5m/1h) instead of click-cycling.
- Composer toolbar moved next to "Send files"; borderless buttons, brand-orange
  active state; pickers open upward and are mobile-friendly.
- Sender bubble background lightened to rgba(249,115,22,0.05).

Removed:
- Panic wipe button (disconnect already wipes keys and clears session state).

Transport unchanged: per-message metadata travels inside the encrypted envelope,
whitelisted/bounded by _sanitizeMessageMeta. Full suite: 19 files, all passing.
Docs (README, CHANGELOG) updated; version bumped to 4.8.20.

manifest.json

@@ -1,5 +1,5 @@
 {
-  "name": "SecureBit.chat v4.8.15 - ECDH + DTLS + SAS",
+  "name": "SecureBit.chat v4.8.20 - ECDH + DTLS + SAS",
   "short_name": "SecureBit",
   "description": "P2P messenger with ECDH + DTLS + SAS security, military-grade cryptography and Lightning Network payments",
   "start_url": "./",