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-ssd-mount.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=Mount the microscope capture SSD
+Documentation=man:mount(8)
+After=systemd-udevd.service
+Before=local-fs.target
+
+[Service]
+# No RemainAfterExit: the unit returns to inactive after each run so that every
+# subsequent plug-in event can start it again. The helper is idempotent, so an
+# already-mounted drive is a no-op.
+Type=oneshot
+ExecStart=/usr/local/sbin/microscope-ssd mount
+TimeoutStartSec=30