release: v4.8.14 secure chat tools (code blocks, view-once, disappearing, unsend, panic)

New privacy-focused messaging controls in the composer:
- Code blocks: button wraps the message in a fenced block; both peers render a
  monospace code window with a copy button (clipboard auto-clears after ~30s).
  Window is built from sanitized text via React nodes — no new XSS surface.
- View-once: recipient sees a blurred bubble, reveals on tap, then it is wiped.
  Honestly cooperative (not screenshot-proof).
- Disappearing messages: optional 30s/5m/1h timer auto-deletes on both sides
  with a live countdown; incoming TTL clamped to [5s, 24h].
- Unsend (delete for everyone) via new MESSAGE_TYPES.message_delete control.
- Panic wipe: clears chat, wipes keys and disconnects (behind a confirm).

Transport:
- Per-message metadata (id / view-once / timer) travels inside the encrypted
  envelope, not in the sanitized text, so content cannot spoof these controls.
- _sanitizeMessageMeta whitelists + bounds metadata on send and receive.
- AAD/replay protection, SAS gate and receive-side DOMPurify are unchanged.

Adds tests/secure-chat-features.test.mjs (full suite: 17 files, all passing).
Bumps version to 4.8.14 across package.json, package-lock.json, manifest.json,
index.html, meta.json, README, SECURITY_DISCLAIMER, header and init banner.

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "securebit-chat",
-  "version": "4.8.13",
+  "version": "4.8.14",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "securebit-chat",
-      "version": "4.8.13",
+      "version": "4.8.14",
       "license": "MIT",
       "dependencies": {
         "base64-js": "1.5.1",