feat(max): add MAX messenger package, sandboxed with Firejail

MAX is the Russian state-affiliated messenger; the official Qt6 client is
repacked from download.max.ru with no independent security track record,
so it never runs unsandboxed. /usr/bin/max is a wrapper (not a symlink)
that always launches through `firejail --profile=max`; the .desktop Exec
goes through the same wrapper so there's no launch path that bypasses it.
The profile hides the rest of the home directory behind private ~/.config,
~/.cache and ~/.local/share/max subdirectories, drops capabilities, enables
seccomp, blocks system D-Bus, and blacklists the standalone crashpad_handler
crash-report uploader. Full elimination of first-party telemetry isn't
claimed or possible from the sandbox layer alone — documented in LICENSE.

Also wires up repo-wide bookkeeping now that all three package changes
(telegram-desktop -> telegram rename, vk-messenger, max) are in: README
package count/catalog rows, docs/maintenance.md naming table and directory
count, and tools/package_updates.sh + tools/validate_repo.py package lists.

max/max.desktop

@@ -0,0 +1,16 @@
+[Desktop Entry]
+Type=Application
+Terminal=false
+Name=MAX
+Exec=/usr/bin/max %U
+Icon=max
+MimeType=x-scheme-handler/max;
+Comment=MAX Messenger Client Application
+Comment[ru]=Клиентское приложение мессенджера MAX
+StartupWMClass=max
+Categories=Chat;Network;InstantMessaging;Qt;
+Keywords=max;chat;im;messaging;messenger;sms;
+DBusActivatable=false
+SingleMainWindow=true
+X-GNOME-UsesNotifications=true
+X-GNOME-SingleWindow=true