Turn the desktop client into a system tray application

Started without a command, keeporg now shows a padlock in the system tray
with a menu like midi-webhook's: a status line, the mirror folder, each
database with its state, Sync Now, browser sign-in and sign-out, the web
interface, the configuration, the log, Start at Login, About and Quit. The
commands are unchanged.

config.json now carries every client setting (device_label,
request_timeout_seconds, ca_file, log_file, notifications), is written in
full on first start and is reloaded by the tray when saved.

A lock in the mirror directory admits one agent at a time, since the tray,
`keeporg run` and a service unit could otherwise race each other.

The tray uses fyne.io/systray: pure Go on Linux, BSD and Windows, cgo on
macOS only. The server keeps no third-party dependencies.

Desktop versions go to 0.5.0.

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

packaging/deb/client/changelog

@@ -1,3 +1,16 @@
+keeporg (0.5.0) unstable; urgency=medium
+
+  * KeepOrg is now a system tray application: started without a command (or 
+    from the applications menu) it shows a padlock whose menu signs in 
+    through the browser, lists each database's state, opens the mirror 
+    folder, the web interface, the settings and the log, and starts at 
+    login. The configuration file now holds every setting (device_label, 
+    request_timeout_seconds, ca_file, log_file, notifications), is written 
+    in full on first start, and is reloaded when saved. Only one agent 
+    synchronizes a mirror directory at a time.
+
+ -- Azer Abdullaev <github@reactorcoremeltdown.anonaddy.com>  Mon, 02 Nov 2026 11:22:07 +0100
+
 keeporg (0.4.0) unstable; urgency=medium
 
   * keeporg db -delete now asks for your account password