Expand compose env vars; add ntfy token + priority + TZ support

docker-compose.yml:
- Every env var documented inline with type/default/purpose
- env_file: .env (required: false) — container starts without it
- NTFY_TOPIC uses :? operator so compose errors clearly if unset
- New vars: NTFY_TOKEN (private topics), NTFY_PRIORITY, TZ, APP_PORT, DEV_PORT
- Removed duplicate NTFY_URL entry

notifier/index.mjs:
- Reads TZ from env (was hardcoded "America/Chicago")
- Reads NTFY_PRIORITY from env (was hardcoded "default")
- Adds Authorization: Bearer header when NTFY_TOKEN is set
- Startup log shows auth status and full schedule config

.env.example: mirrors every compose variable with descriptions

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

.env.example

@@ -1,17 +1,38 @@
-# Copy to .env and fill in your values
+# Copy this file to .env and fill in your values.
+# docker-compose reads .env automatically for variable substitution.
 
-# ntfy topic — make it unguessable (anyone who knows it can receive/send)
-# Subscribe at https://ntfy.sh/YOUR_TOPIC or in the ntfy app
+# ── App ────────────────────────────────────────────────────────────────────────
+# Port the web app is exposed on (default: 8080)
+APP_PORT=8080
+
+# ── ntfy ──────────────────────────────────────────────────────────────────────
+# Required — your ntfy topic. Keep it unguessable (anyone with the name can sub).
+# Subscribe at https://ntfy.sh/YOUR_TOPIC or in the ntfy iOS/Android app.
 NTFY_TOPIC=your-unguessable-topic-here
 
-# Optional: self-hosted ntfy server
-# NTFY_URL=https://ntfy.sh
+# ntfy server — leave as-is for ntfy.sh, or point to your self-hosted instance
+NTFY_URL=https://ntfy.sh
 
-# Optional: URL the notification links back to (your deployed app)
-# APP_URL=http://localhost:8080
+# Bearer token for private/access-controlled topics (leave blank for public)
+NTFY_TOKEN=
 
-# Optional: cron schedule (default: 9 AM on the 1st of every month)
-# CRON_SCHEDULE=0 9 1 * *
+# Notification priority: min | low | default | high | urgent
+NTFY_PRIORITY=default
 
-# Set to "true" to get a test ping the moment the notifier starts
-# NTFY_TEST_ON_START=false
+# ── Schedule ──────────────────────────────────────────────────────────────────
+# Cron schedule for the monthly reminder (default: 9 AM on the 1st of each month)
+# Format: minute hour day-of-month month day-of-week
+CRON_SCHEDULE=0 9 1 * *
+
+# IANA timezone for the cron schedule
+TZ=America/Chicago
+
+# URL the notification deep-links back to
+APP_URL=http://localhost:8080
+
+# Set to "true" to fire a test notification the moment the notifier container starts
+NTFY_TEST_ON_START=false
+
+# ── Dev ───────────────────────────────────────────────────────────────────────
+# Port for the Vite dev server (docker compose --profile dev up dev)
+DEV_PORT=5173