feat: harden dashcam transfer tegen flakke SD-lezer + stale-mount cleanup

- dashcam-transfer.py: log echte OSError (shutil.copy2 i.p.v. cp), pre-flight
  leesbaarheidscheck voor ruimte-wissen, retry (3x) + early-abort (5x), guards
  op bestandssysteem-calls, WhatsApp GESTOPT bij defecte kaart
- dashcam-transfer-mount.sh: skip als service al draait, read-only fsck.exfat
  health check, %k device-naam doorgeven
- dashcam-transfer-cleanup.sh: nieuw - ruimt stale mount op bij udev REMOVE
- udev/99-dashcam-trigger.rules: ADD + REMOVE regels met %k
- tests: 20 python + 7 mount + 12 cleanup checks
- README: architectuur, robuustheid, deploy-instructies

dashcam-transfer-cleanup.sh

@@ -0,0 +1,39 @@
+#!/bin/bash
+# Remove-trigger cleanup for the dashcam SD card.
+# Called by udev rule 99-dashcam-trigger.rules via systemd-run on
+# ACTION=="remove" with %k as $1. Unmounts a stale /mnt/sdcard mount and
+# stops a transfer that can no longer complete.
+# Idempotent: does nothing when /mnt/sdcard is not mounted or still healthy.
+logger -t dashcam-transfer "Remove trigger: block device weggevallen"
+
+src=$(findmnt -no SOURCE /mnt/sdcard 2>/dev/null)
+if [ -z "$src" ]; then
+    logger -t dashcam-transfer "Remove: /mnt/sdcard niet gemount, niets te doen"
+    exit 0
+fi
+
+case "$src" in
+    /*) ;;
+    *) logger -t dashcam-transfer "Remove: onbekende source ($src), niets te doen"; exit 0 ;;
+esac
+
+stale=0
+if [ ! -e "$src" ]; then
+    stale=1
+elif [ -n "$1" ] && [[ "$src" == *"/$1"* ]]; then
+    stale=1
+fi
+
+if [ "$stale" -eq 0 ]; then
+    logger -t dashcam-transfer "Remove: device $src nog aanwezig, mount blijft"
+    exit 0
+fi
+
+logger -t dashcam-transfer "Remove: device $src verdwenen — transfer stoppen, mount opruimen"
+systemctl stop dashcam-transfer.service 2>/dev/null || true
+sleep 1
+if ! umount /mnt/sdcard 2>/dev/null; then
+    logger -t dashcam-transfer "Remove: umount mislukt, lazy unmount"
+    umount -l /mnt/sdcard 2>/dev/null || true
+fi
+logger -t dashcam-transfer "Remove: stale mount opgeruimd"