Release 0.6.2 + AppImage packaging

Bump to 0.6.2 (Cargo + Inno .iss), promote CHANGELOG [Unreleased] -> [0.6.2].
0.6.2 rolls up the licensing (MIT + THIRD_PARTY_LICENSES) and the friends-list
liveness fixes (active offline marking, 15s refresh, manual Rescan) on the
0.6.x wire format (gossip v5, compatible with 0.6.0/0.6.1).

Adds packaging/appimage: a thin AppImage recipe (linuxdeploy) that bundles the
pixelpass screen-share helper in usr/bin so peerspeak's $PATH lookup finds it
with no code change. Assets are include_bytes!-embedded; the graphics stack and
pixelpass's gstreamer/mpv tools are left to the host. Built on Ubuntu 24.04
(glibc 2.39) for reach across Debian 13+/Fedora 40+/rolling.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Cargo.lock

@@ -4871,7 +4871,7 @@ checksum = "35fb2e5f958ec131621fdd531e9fc186ed768cbe395337403ae56c17a74c68ec"
 
 [[package]]
 name = "peerspeak"
-version = "0.6.1"
+version = "0.6.2"
 dependencies = [
  "anyhow",
  "async-trait",