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.

doc/SECURITY-ARCHITECTURE.md

@@ -10,6 +10,7 @@
 | Privacy mode | optional TURN relay-only mode |
 | Message UI safety | incoming decrypted text sanitized before display |
 | File transfer | validated metadata, explicit consent, allowlist policy |
+| Voice messages | same chunked AES-GCM transfer as files; auto-accepted and played inline |
 | Local metadata | encrypted IndexedDB envelopes with migration |
 | Lifecycle | unified disconnect cleanup and bounded resource retention |
 
@@ -42,6 +43,18 @@ The verified state is reached only when both local and remote confirmation flags
 5. sender transmits chunks only after acceptance
 6. completed received buffers are retained within a bounded window
 
+## Voice messages
+
+Voice notes reuse the file-transfer pipeline, so they inherit its per-file
+AES-GCM session key, chunking, and SHA-256 integrity check. Differences from a
+regular file:
+
+1. audio is recorded in-browser and encoded as PCM/WAV before sending
+2. duration and a downsampled waveform travel as **unsigned** presentation
+   metadata; the audio bytes remain integrity-protected by the signed file hash
+3. the receiver **auto-accepts** voice transfers (no consent prompt) and plays
+   them inline from an in-memory blob — nothing is written to disk
+
 ## Disconnect cleanup
 
 The canonical disconnect path clears: