chore(release): bump to 0.5.0 + add CHANGELOG

Version bump 0.4.0 -> 0.5.0 (Cargo.toml/lock, Windows .iss, PKGBUILD
placeholder) and a new CHANGELOG.md covering the 21 commits since v0.4.0
(A9 context menu, W21 selectable text, A25 clock-skew, A23 screen-share
per-app audio, A15 reliable critical commands, A24 per-peer volume,
Tier-C security caps, Debian/Arch packaging).

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

packaging/PKGBUILD

@@ -1,7 +1,7 @@
 # Maintainer: mollusk <jitty+lc1iz0dc@protonmail.com>
 pkgname=peerspeak-git
 _pkgname=peerspeak
-pkgver=0.4.0.r254.g913b0b6
+pkgver=0.5.0.r0.g0000000
 pkgrel=1
 pkgdesc="Decentralized peer-to-peer voice chat (Rust/iroh/PipeWire/Opus/iced)"
 arch=('x86_64')

packaging/windows/peerspeak.iss

@@ -12,7 +12,7 @@
 ; (x86_64-pc-windows-gnu, statically linked -- no extra DLLs needed).
 
 #define MyAppName "PeerSpeak"
-#define MyAppVersion "0.4.0"
+#define MyAppVersion "0.5.0"
 #define MyAppPublisher "mollusk"
 #define MyAppExeName "peerspeak.exe"