Switch to Noctalia v5 and fix niri startup

Fix Mod+T bind (one action per bind), launch noctalia v5 from autostart,
port keybinds to `noctalia msg`, add config.toml, changelog and docs.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

niri/cfg/autostart.kdl

@@ -1,5 +1,5 @@
 // ────────────── Startup Applications ──────────────
 // https://github.com/YaLTeR/niri/wiki/Configuration:-Miscellaneous#spawn-sh-at-startup
 
-    spawn-sh-at-startup "qs -c noctalia-shell"
+    spawn-at-startup "noctalia"
     spawn-at-startup "kanshi"