Add end-to-end encrypted voice messages; release v5.4.5

- Record voice notes in-browser, sent over the chunked AES-GCM file-transfer
  channel (per-file session key + signed SHA-256 integrity).
- Captured as PCM and encoded to WAV for universal playback (incl. iOS/Safari);
  auto-accepted and played inline from an in-memory blob, never written to disk.
- Composer mic button with live waveform + timer; desktop shows mic + send side
  by side, mobile swaps mic to send when typing.
- CSP media-src now allows blob: so recorded/received audio can play.
- Roadmap: Desktop Edition -> 5.0, new 5.5 'Secure Voice & Calls', later
  milestones shifted; version bumped to 5.4.5.
- Update README, docs (security/API/cryptography), and CHANGELOG.

src/styles/animations.css

@@ -27,3 +27,15 @@
     0% { transform: translateX(0); }
     100% { transform: translateX(-50%); }
 }
+
+/* ── Voice messages ─────────────────────────────────────────────── */
+/* Pulsing red REC dot while recording. */
+@keyframes vmRec {
+    0%, 100% { opacity: 1; transform: scale(1); }
+    50% { opacity: 0.35; transform: scale(0.82); }
+}
+/* Expanding ring behind the record button. */
+@keyframes vmRing {
+    0% { transform: scale(1); opacity: 0.5; }
+    100% { transform: scale(2.1); opacity: 0; }
+}