desktop: an agent and a mini timer, not an application window

The design of the full desktop app was still bad, and the reason it stayed bad
is that it had no business existing. Five pages — Timer, Tasks, Blocker, Report,
Settings — each a second view of the *server's* data: a second place to be
wrong, a second place to style, and a second place to keep in step with a web
app that already does lists, rules and reports properly in a browser, on any
device. So it is gone, along with 2,100 lines of QML and the controller surface
that fed it.

What is left is what only a program on your machine can do, plus the two
surfaces worth having in front of you:

* **the tray menu — unchanged**, as asked. All fourteen entries, plus
  "Settings…". "Open Kadence" now brings the countdown up, because that is what
  it meant all along.
* **the mini timer**, which is now the whole of this app's own interface and so
  finally carries the house style on its own: warm surface, hairline instead of
  shadow, a letterspaced eyebrow, the progress lane as a rule, and exactly one
  filled button — whichever action is the obvious next one. The countdown is set
  in the display serif on a **fixed advance**, because Fraunces has no tabular
  figures and ships no `tnum`: each glyph now sits in a box as wide as the widest
  digit, instead of the clock shifting sideways on every tick. The phone client
  documents the same trap; the desktop had it too and nobody had looked.
  It also says OFFLINE when the backend is away — the count and the clock are
  both the server's, and this is the only window left to say it in.
* **a settings dialog**, because a fresh install has to be pointed at a backend
  somewhere. One column, hairline sections: the backend and its token, where the
  mini timer sits, what this machine enforces, and what it does to the session.
  It edits `desktop.json` and nothing else — with one honest exception, view-only
  mode, which is a server-side flag the other clients have to honour too.

Structurally, `app.py` no longer loads a QML root at all: a plain `QQmlEngine`
with the mini timer as a component, and the dialog built on demand. Everything
that used to ask "is the main window visible?" is simpler for not having one —
the mini timer's auto-show rule is now just "an interval is running", which is
what the setting always claimed.

The window-only controller surface goes with the pages: tasks and task writes,
stats, the daily report, the settings document, the presets, the cycle and
interruption counters, and their worker jobs and API calls. Two things were kept
deliberately: the task list is still read once a minute for one fact — which task
is pinned, so "Start focus" from the tray attaches what you pinned this morning —
and `timerEnabled` now comes from the timer state, which already carries
`timer_enabled`, rather than from a second fetch of a document this app can no
longer edit.

Also: `--settings` and a `Settings` D-Bus verb; toasts go to the tray's balloon
now that the snackbar is gone; the launcher entry starts the agent and grew a
Settings action; a systemd user unit is shipped rather than only written at
runtime; and both READMEs say what this piece is.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

desktop/packaging/kadence-desktop.service

@@ -0,0 +1,32 @@
+# The agent, as a systemd user service.
+#
+# Kadence on the desktop is a tray agent: it enforces the server's blocking
+# policy on this machine, posts notifications with buttons, answers D-Bus and
+# shows a floating countdown. None of that needs a window, so running it from
+# login is the normal arrangement — `--minimized` starts it with nothing on
+# screen and the mini timer appears by itself when an interval starts.
+#
+# Settings -> "Run as a systemd user service" writes this same unit with an
+# absolute ExecStart; this copy is for installing it by hand:
+#
+#     mkdir -p ~/.config/systemd/user
+#     cp desktop/packaging/kadence-desktop.service ~/.config/systemd/user/
+#     systemctl --user daemon-reload
+#     systemctl --user enable --now kadence-desktop
+#     journalctl --user -u kadence-desktop -f
+#
+# `PartOf`/`WantedBy=graphical-session.target` because the tray, the
+# notifications and the KWin rule all need a session to be in.
+[Unit]
+Description=Kadence desktop client
+PartOf=graphical-session.target
+After=graphical-session.target
+
+[Service]
+Type=simple
+ExecStart=%h/.local/bin/kadence-desktop --minimized
+Restart=on-failure
+RestartSec=5
+
+[Install]
+WantedBy=graphical-session.target