Candidate 1: the rising edge of an authentication sends the touch event only

Labelled baseline on the proven loop, quick taps only: enrolled finger 2 of 10,
wrong finger 0 of 5. Every press was one frame.

The rising-edge frame costs ~700 ms because it runs the matcher twice -- event 5
and event 7 on the same image, two verdicts back. A human tap is over before a
second frame can exist at that cost. Keeping only the touch event keeps what
every recorded match followed, halves the rising frame, and may be the
difference between one frame per tap and two. It is a single variable against a
labelled baseline; if the rate drops, it comes out.

Also fixes fptrial.sh's latency column, which was all zero: busybox date has no
%N, so it reads /proc/uptime instead.

packaging/fptrial.sh

@@ -9,7 +9,7 @@
 # is the latency a user feels. Unlabelled runs cannot be turned into a rate.
 C=${1:-10}; W=${2:-5}
 OUT=/tmp/fptrial-$(date +%Y%m%d-%H%M%S).log
-now() { date +%s%N; }
+now() { awk '{gsub(/\./,""); print $1 "0000000"}' /proc/uptime; }
 run() {  # $1 = label
     printf '\n>>> %s -- press and LIFT (quick tap) ... ' "$1"
     t0=$(now)