Microscope camera kiosk

Touchscreen kiosk for the Raspberry Pi HQ camera (IMX477) used as a
microscope: live preview from boot, raw frame recording, full-resolution
stills, and automatic capture-SSD mounting.

- app.py: GTK3 fullscreen UI over cage — preview, REC/STOP, PHOTO,
  90-degree rotate button, tap-to-open exposure/gain/settings sliders,
  and an "SSD NOT MOUNTED" badge
- camera.py: picamera2 wrapper with separate video (ISP preview + packed
  12-bit raw) and still (4056x3040) configurations
- recorder.py: writer thread turning the raw stream into one Bayer frame
  per file plus index.jsonl/session.json, with dropped/missed accounting
- photos.py: still capture to DNG + JPEG, and a background worker that
  renders a viewable 16-bit sRGB TIFF from the 12-bit Bayer frame
- storage.py: SSD mount state and the date/time/format session layout
- tools/unpack_raw.py: desktop-side unpacker/demosaicer
- system/ + install.sh: systemd units, udev rule, mount helper, sudoers

Note: raw frames are written byte-for-byte as the sensor produced them, so
they stay decodeable regardless of how the stills pipeline evolves.

system/microscope-camera.service

@@ -0,0 +1,35 @@
+[Unit]
+Description=Microscope camera kiosk (cage + capture UI)
+Documentation=file:/opt/microscope-camera/README.md
+After=systemd-user-sessions.service systemd-logind.service
+Wants=systemd-logind.service
+Conflicts=getty@tty1.service
+After=getty@tty1.service
+ConditionPathExists=/opt/microscope-camera/app.py
+
+[Service]
+Type=simple
+User=tyler
+Group=tyler
+# A logind session on tty1 gives cage DRM master plus input device access.
+PAMName=login
+TTYPath=/dev/tty1
+TTYReset=yes
+TTYVHangup=yes
+TTYVTDisallocate=yes
+StandardInput=tty
+StandardOutput=journal
+StandardError=journal
+Environment=XDG_RUNTIME_DIR=/run/user/1000
+Environment=HOME=/home/tyler
+Environment=PYTHONUNBUFFERED=1
+ExecStartPre=/bin/sh -c 'install -d -m 700 -o tyler -g tyler /run/user/1000'
+ExecStart=/usr/bin/cage -s -- /usr/bin/python3 /opt/microscope-camera/app.py
+Restart=always
+RestartSec=2
+# Keep the recorder alive long enough to flush its last frames on restart.
+KillSignal=SIGTERM
+TimeoutStopSec=30
+
+[Install]
+WantedBy=multi-user.target