feat: session file registry with drag-and-drop on day view

Adds a FileDropZone at the bottom of the day view where users can
drop all session files at once. Filenames are regex-matched to
subjects using their animal_id_string (word-boundary aware, so
"2852" won't match "28520"). Only metadata is recorded — files
are never uploaded.

Backend: new session_files table (id, daily_status_id, filename,
file_size BIGINT, file_type, last_modified, notes). Routes:
  POST /api/daily-statuses/:id/files  (batch create)
  GET  /api/daily-statuses/:id/files
  DELETE /api/session-files/:id

Frontend: FileDropZone shows per-subject match groups, unmatched
files, and a warning for subjects with no match. After saving,
registered files are displayed with delete capability.

test-files/: generate_test_files.sh creates 4 dummy files per
subject (2×bin, 2×csv) with correct naming for drag-and-drop
testing. Pre-generated for 2026-04-23 with IDs 2852/3076/3077/3078.

Tests: 19 tests covering drag state, regex matching, save payload,
partial-overlap prevention, multi-subject batching, and delete.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test-files/generate_test_files.sh

@@ -0,0 +1,75 @@
+#!/bin/bash
+# Generates dummy session files for drag-and-drop testing on the day view.
+# Files are tiny (just named correctly) — the browser File API only reads metadata.
+#
+# Usage:  bash generate_test_files.sh [DATE] [IDS...]
+#   DATE   defaults to today (YYYY-MM-DD)
+#   IDS    defaults to the three real subject IDs from the reach-task experiment
+#
+# Output: ./session_files/<DATE>/
+
+DATE=${1:-$(date +%Y-%m-%d)}
+shift
+SUBJECTS=("${@}")
+
+if [ ${#SUBJECTS[@]} -eq 0 ]; then
+  # Default IDs matching the real subjects in the experiments database
+  # (animal_id_string values visible on the day view)
+  SUBJECTS=("2852" "3076" "3077" "3078")
+fi
+
+OUTDIR="./session_files/${DATE}"
+mkdir -p "$OUTDIR"
+
+echo "Generating test files in ${OUTDIR}/ for subjects: ${SUBJECTS[*]}"
+echo ""
+
+for ID in "${SUBJECTS[@]}"; do
+  # File 1: large binary session recording (~placeholder, 0 bytes in test)
+  # Real file would be ~10 GB (e.g. raw ephys .bin)
+  BIN1="${OUTDIR}/${DATE}_${ID}_ephys_raw.bin"
+  touch "$BIN1"
+  echo "  [~10 GB] ${DATE}_${ID}_ephys_raw.bin"
+
+  # File 2: large HDF5 spike-sorted output (~placeholder, 0 bytes in test)
+  # Real file would be ~10 GB (e.g. kilosort output .h5)
+  BIN2="${OUTDIR}/${DATE}_${ID}_kilosort.h5"
+  touch "$BIN2"
+  echo "  [~10 GB] ${DATE}_${ID}_kilosort.h5"
+
+  # File 3: CSV trial events (~10 MB real, 1 KB here)
+  CSV1="${OUTDIR}/${DATE}_${ID}_trials.csv"
+  {
+    echo "trial_num,timestamp,outcome,reaction_time_ms,reward"
+    for i in $(seq 1 20); do
+      OUTCOME=$( [ $((RANDOM % 3)) -eq 0 ] && echo "Failure" || echo "Success" )
+      printf "%d,%.3f,%s,%d,%d\n" \
+        "$i" "$(echo "$i * 0.823 + 1.0" | bc -l 2>/dev/null || echo $i)" \
+        "$OUTCOME" "$((RANDOM % 400 + 50))" "$((RANDOM % 2))"
+    done
+  } > "$CSV1"
+  echo "  [~10 MB] ${DATE}_${ID}_trials.csv"
+
+  # File 4: CSV behavioral log (~10 MB real, small here)
+  CSV2="${OUTDIR}/${DATE}_${ID}_behavior_log.csv"
+  {
+    echo "ts,event,value,notes"
+    echo "0.000,session_start,1,"
+    echo "1.234,trial_start,1,"
+    echo "1.856,reach_onset,1,"
+    echo "2.102,reach_end,1,"
+    echo "2.103,outcome,Success,"
+    echo "3.500,trial_start,2,"
+    echo "4.100,reach_onset,1,"
+    echo "4.950,outcome,Failure,"
+    echo "9999.9,session_end,1,"
+  } > "$CSV2"
+  echo "  [~10 MB] ${DATE}_${ID}_behavior_log.csv"
+  echo ""
+done
+
+TOTAL=$(find "$OUTDIR" -type f | wc -l)
+echo "Done — ${TOTAL} files in ${OUTDIR}/"
+echo ""
+echo "Drag the entire '${DATE}' folder into the day-view drop zone at:"
+echo "  https://experiments.sam-tran.com/experiments/<id>/day/${DATE}?field=<fieldId>"