Turn the demo app into a Canon 450D intervalometer

Replaces the gPhoto2 demo UI (live view beside the raw config tree) with a
timelapse intervalometer. The home screen carries only what changes between
runs - interval, frame count, start delay, start/stop, countdown, progress
and a log - while every camera setting moves into a settings drawer.

- intervalometer.js: schedules frames on an absolute grid (start + n *
  interval) so transfer time doesn't accumulate as drift over a long run. An
  overrun logs and fires as soon as the camera is free rather than dropping a
  frame; three consecutive failures abort.
- storage.js: frames stream into a folder via the File System Access API,
  named for capture time (20260801-172713_00001.JPG) so sorting by name is
  sorting by time. Falls back to downloads. Also holds the screen wake lock,
  since background tabs get their timers throttled.
- config-utils.js: config tree lookups, shutter speed parsing, and bulb
  capability detection (bulb toggle or Canon eosremoterelease).
- home.js: sequence controls plus a read-only exposure readout and pre-flight
  warnings when the interval can't fit the exposure and transfer.
- settings.js / index.js: app prefs and the full config tree behind a drawer.
  Config polling now only runs while that drawer is open, leaving the USB link
  to the captures during a sequence.

Live view stays up between frames and steps aside only while the shutter
fires, which is what the EOS driver requires; it recovers afterwards with
backoff instead of hammering a busy camera.

Deployed as an assets-only Cloudflare Worker. The WASM is built with pthreads
and allocates a shared WebAssembly.Memory, so _headers reproduces the COOP/COEP
pair from serve.json - without cross-origin isolation the app fails to start.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QK7PKpRVoy69Fpa32R8abb

examples/preact/config-utils.js

@@ -0,0 +1,109 @@
+/*
+ * Copyright 2021 Google LLC
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+/** @typedef {import('web-gphoto2').Config} Config */
+
+/**
+ * Depth-first lookup of a config node by its gphoto2 name.
+ * @param {Config | undefined} config
+ * @param {string} name
+ * @returns {Config | undefined}
+ */
+export function findConfig(config, name) {
+  if (!config) return undefined;
+  if (config.name === name) return config;
+  if (config.type !== 'window' && config.type !== 'section') return undefined;
+  for (let child of Object.values(config.children)) {
+    let found = findConfig(child, name);
+    if (found) return found;
+  }
+  return undefined;
+}
+
+/**
+ * Read the current value of a config node, if it exists.
+ * @param {Config | undefined} config
+ * @param {string} name
+ */
+export function configValue(config, name) {
+  let node = findConfig(config, name);
+  return node && 'value' in node ? node.value : undefined;
+}
+
+/**
+ * The read-only summary shown at the bottom of the home screen. These are the
+ * names the Canon EOS driver (450D included) exposes; anything missing is
+ * simply skipped, so this stays useful on other bodies too.
+ * @param {Config | undefined} config
+ */
+export function statusReadout(config) {
+  return [
+    ['Mode', 'autoexposuremode'],
+    ['Shutter', 'shutterspeed'],
+    ['Aperture', 'aperture'],
+    ['ISO', 'iso'],
+    ['Format', 'imageformat'],
+    ['Battery', 'batterylevel'],
+    ['Shots left', 'availableshots'],
+    ['Target', 'capturetarget']
+  ]
+    .map(([label, name]) => ({ label, value: configValue(config, name) }))
+    .filter(({ value }) => value !== undefined && value !== '');
+}
+
+/**
+ * Turn a gphoto2 shutter speed string ("1/250", "30", "0.3", "bulb") into
+ * seconds. Returns undefined when it can't be parsed.
+ * @param {unknown} value
+ */
+export function shutterSpeedSeconds(value) {
+  if (typeof value !== 'string') return undefined;
+  let str = value.trim().toLowerCase();
+  if (str === 'bulb' || str === '') return undefined;
+  let fraction = /^(\d+(?:\.\d+)?)\/(\d+(?:\.\d+)?)$/.exec(str);
+  if (fraction) {
+    let denominator = Number(fraction[2]);
+    return denominator ? Number(fraction[1]) / denominator : undefined;
+  }
+  let seconds = Number(str.replace(/s$/, ''));
+  return Number.isFinite(seconds) ? seconds : undefined;
+}
+
+/**
+ * How the camera can be held open for a long exposure, if at all.
+ *
+ * `bulb` is a plain toggle on many bodies; Canon EOS bodies instead drive the
+ * shutter through `eosremoterelease`. Returns null when neither is available.
+ * @param {Config | undefined} config
+ * @returns {{ kind: 'bulb' } | { kind: 'eosremoterelease', press: string, release: string } | null}
+ */
+export function detectBulbSupport(config) {
+  let bulb = findConfig(config, 'bulb');
+  if (bulb && bulb.type === 'toggle' && !bulb.readonly) {
+    return { kind: 'bulb' };
+  }
+  let remote = findConfig(config, 'eosremoterelease');
+  if (remote && remote.type === 'menu' && !remote.readonly) {
+    let press = remote.choices.find(c => /^press full/i.test(c));
+    let release = remote.choices.find(c => /^release full/i.test(c));
+    if (press && release) {
+      return { kind: 'eosremoterelease', press, release };
+    }
+  }
+  return null;
+}