chore: add generated pattern previews and time-based LED brightness script

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/led_brightness_by_time.sh

@@ -0,0 +1,72 @@
+#!/usr/bin/env bash
+# Set DW LED brightness based on time of day.
+# Intended to be run from cron every minute, e.g.:
+#   * * * * * /Volumes/4TB\ SSD/projects/dune-weaver/scripts/led_brightness_by_time.sh >> /tmp/dw-led-brightness.log 2>&1
+#
+# Anchors below are (HH:MM, brightness 0-100). Brightness is linearly
+# interpolated between consecutive anchors, so the LEDs ramp smoothly.
+
+set -euo pipefail
+
+API="${DW_API:-http://localhost:8080}"
+ENDPOINT="$API/api/dw_leds/brightness"
+
+# Edit these to taste. Must be sorted by time. First and last bracket midnight.
+ANCHORS=(
+  "00:00 5"    # deep night: dim glow
+  "06:30 15"   # pre-dawn: warm wake-up level
+  "08:00 60"   # morning: full ambient
+  "12:00 90"   # midday peak
+  "18:00 70"   # evening
+  "21:30 30"   # wind-down
+  "23:30 5"    # back to deep night
+)
+
+now_minutes() {
+  local h m
+  h=$(date +%H)
+  m=$(date +%M)
+  # base-10 force avoids "08" being parsed as octal
+  echo $(( 10#$h * 60 + 10#$m ))
+}
+
+anchor_minutes() { # "HH:MM <bri>" -> minutes
+  local t=${1%% *}
+  local h=${t%%:*}
+  local m=${t##*:}
+  echo $(( 10#$h * 60 + 10#$m ))
+}
+
+anchor_value() { echo "${1##* }"; }
+
+compute_brightness() {
+  local now=$1 prev_t prev_v next_t next_v
+  for ((i = 0; i < ${#ANCHORS[@]} - 1; i++)); do
+    prev_t=$(anchor_minutes "${ANCHORS[i]}")
+    next_t=$(anchor_minutes "${ANCHORS[i+1]}")
+    if (( now >= prev_t && now <= next_t )); then
+      prev_v=$(anchor_value "${ANCHORS[i]}")
+      next_v=$(anchor_value "${ANCHORS[i+1]}")
+      # linear interpolation, integer math
+      echo $(( prev_v + (next_v - prev_v) * (now - prev_t) / (next_t - prev_t) ))
+      return
+    fi
+  done
+  # fallback: last anchor's value
+  anchor_value "${ANCHORS[-1]}"
+}
+
+main() {
+  local now bri
+  now=$(now_minutes)
+  bri=$(compute_brightness "$now")
+
+  echo "[$(date -Iseconds)] minute=$now brightness=$bri"
+
+  curl -fsS -X POST "$ENDPOINT" \
+    -H 'Content-Type: application/json' \
+    -d "{\"value\": $bri}"
+  echo
+}
+
+main "$@"