Initial commit: notifications, monitoring, on-call and incidents

One binary and one SQLite file. Topics with ntfy-style publish and
subscribe, HTTP/TCP/DNS/TLS/heartbeat monitors with a public status page,
schedules and escalation policies, and incidents with a timeline and
post-mortem. The UI follows the Lightwell design language.

Builds against an unreleased Reef (secretbox) through a local replace line.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.env.example

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+# Copy this file to .env and fill it in. Sandbar reads .env from its working directory
+# (or pass -env /path/to/file). Real environment variables always win over the file.
+# Never commit .env.
+
+# Encrypts saved secrets (channel webhook URLs and email addresses) inside the database.
+# Generate one with:  sandbar -genkey
+# Keep it apart from the data folder and back it up: without it those secrets cannot be read.
+# If you leave it unset, a key is generated into <data>/master.key instead.
+SANDBAR_MASTER_KEY=
+
+# Creates the first administrator at startup (otherwise use the setup page in the browser).
+#SANDBAR_ADMIN_EMAIL=you@example.com
+#SANDBAR_ADMIN_PASSWORD=
+
+# Address to listen on, and the folder for the database.
+#SANDBAR_LISTEN=:8090
+#SANDBAR_DATA=./sandbar-data
+
+# Public address people use to reach Sandbar. Links in notifications use it.
+#SANDBAR_URL=https://sandbar.example.com
+
+# Serves Prometheus metrics at /metrics for a scraper that sends this as a bearer token.
+# Leave empty and /metrics does not exist.
+#SANDBAR_METRICS_TOKEN=
+
+# How long topic messages and monitor results are kept, in days.
+#SANDBAR_MESSAGE_DAYS=30
+#SANDBAR_CHECK_DAYS=30
+
+# Outgoing email, for email channels and for paging people by email.
+#SANDBAR_SMTP_HOST=smtp.example.com
+#SANDBAR_SMTP_PORT=587
+#SANDBAR_SMTP_USER=
+#SANDBAR_SMTP_PASSWORD=
+#SANDBAR_SMTP_FROM=sandbar@example.com