Become a daemon: a held session, a worker, and net.reactivated.Fprint

The probe becomes the thing the plan was for. Three threads: the supplicant
services QTEE's callbacks; the worker owns the sensor rail, the QTEE session
and the trustlet and is the only thread that ever invokes it, so every
enrolment and authentication is serialised by construction; the main thread
runs the GLib loop and speaks fprintd's own D-Bus interface, never touching
the trustlet directly.

Session is the bring-up from a cold /dev/tee0 to a calibrated sensor, plus the
enrol and verify loops as methods that take a cancel flag and progress
callbacks. Worker is a job queue on a pthread with an 8 MiB stack -- musl's
default is 128 KiB and the session keeps request buffers on the stack. Results
come back through g_idle_add so signals are emitted on the thread that owns
the connection.

net.reactivated.Fprint is implemented rather than wrapped: Manager with
GetDevices/GetDefaultDevice, Device with Claim/Release, EnrollStart/Stop,
VerifyStart/Stop, ListEnrolledFingers and the three Delete variants, the three
signals, and the five properties. Owning fprintd's name is what lets
pam_fprintd, the Plasma KCM and fprintd-enroll work unmodified.

Two honest limits. Authorisation is the conservative rule -- you may act on
your own prints, root on anyone's -- because polkit is not in this milestone.
And DeleteEnrolledFingers removes the finger's NAME only: FF_CMD_TA_REMOVE
exists but its payload is not reverse-engineered, and guessing at a command
that writes to the store is exactly how an index got invalidated earlier
today. A deleted finger loses its name and stops being offered; its template
still occupies a slot in the group. Logged as such.

The finger-name map is written per user under the state directory, tmp-file
and rename. An enrolment records the fid the trustlet reported in the touch
event's response; if none was reported the finger cannot be named yet, and
the daemon says so rather than inventing one.

Verified on the phone as a systemd unit: owns the bus name, init chain
complete, floor calibrated, ready.

packaging/net.reactivated.Fprint.conf

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?> <!--*-nxml-*-->
+<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
+ "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
+<!-- SPDX-License-Identifier: GPL-3.0-only
+     SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+     fingerprintd owns fprintd's bus name so pam_fprintd, the Plasma KCM and
+     fprintd-enroll work unmodified. Same shape as fprintd's own policy: root
+     owns the name, anyone may call it, and the daemon enforces who may act on
+     whose prints.
+     Install: /usr/share/dbus-1/system.d/net.reactivated.Fprint.conf -->
+<busconfig>
+  <policy user="root">
+    <allow own="net.reactivated.Fprint"/>
+    <allow send_destination="net.reactivated.Fprint"/>
+  </policy>
+  <policy context="default">
+    <allow send_destination="net.reactivated.Fprint"/>
+    <allow receive_sender="net.reactivated.Fprint"/>
+  </policy>
+</busconfig>