Add barrier_picker_app — Dockerised web picker for barrier opening

A FastAPI app + plain HTML5 video page that replaces the matplotlib
picker. Browse to http://host:8000/, scrub through each video with
arrow keys (±5 s, ±1 s with Shift, ±0.1 s with Ctrl, ±1 frame with
,/.), and click one of three buttons:
  - All barriers open      — every ROI usable
  - Upper barrier opens    — ROIs 1,3,5 usable; lower row marked bad
  - Lower barrier opens    — ROIs 2,4,6 usable; upper row marked bad

The current playhead time is recorded as opening_s; bad_rois is set
accordingly. Also keyboard shortcuts (1/2/3 for the three modes,
s/u for skip/unusable). Refresh-safe: every submission persists to
data/metadata/barrier_opening.csv before advancing.

Server uses byte-range streaming so seeking inside long videos is
fast. Dockerfile + docker-compose.yml mount the data volume RO and
the metadata folder RW.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/barrier_picker_app/docker-compose.yml

@@ -0,0 +1,21 @@
+services:
+  picker:
+    build: .
+    image: cupido-barrier-picker
+    container_name: cupido-barrier-picker
+    ports:
+      - "8000:8000"
+    volumes:
+      # Project data volume (videos + tracking DBs + merged TSV) — read-only.
+      - /mnt/data/projects/cupido:/mnt/data/projects/cupido:ro
+      # Source video tree — mount at the same path the inventory references
+      # (so the mp4_path strings in video_inventory.csv resolve unchanged).
+      - /mnt/ethoscope_data/videos:/mnt/ethoscope_data/videos:ro
+      # Repo's data/metadata folder — mount read-write so the app can persist
+      # barrier_opening.csv. Adjust the host path to your local checkout.
+      - ../../data/metadata:/cupido/data/metadata:rw
+    environment:
+      CUPIDO_DATA_VOLUME: /mnt/data/projects/cupido
+      CUPIDO_INVENTORY_CSV: /cupido/data/metadata/video_inventory.csv
+      CUPIDO_OUTPUT_CSV: /cupido/data/metadata/barrier_opening.csv
+    restart: unless-stopped