feat(standalone): support Redis Sentinel connections

[omarzeineddine-ai]

Problem

Closes #44

The standalone Docker image only accepts REDIS_URL, so Sentinel-managed Redis deployments can't use it — there's no way to hand BullMQ a sentinel connection.

Solution

Connection config moves to a small, tested connectionFromEnv() module with two modes:

Variable	Role
REDIS_SENTINELS	Comma-separated host:port list (port defaults to 26379). Enables Sentinel mode.
REDIS_SENTINEL_NAME	Master group name (e.g. mymaster). Required with REDIS_SENTINELS.
REDIS_SENTINEL_PASSWORD	Auth for the sentinel nodes themselves.
REDIS_USERNAME / REDIS_PASSWORD / REDIS_DB	Optional, apply to both modes.

ioredis (via BullMQ) resolves the current master through the listed sentinels and follows failovers automatically. The same connection object flows into the alert store, so alert persistence follows the master too.

REDIS_URL behavior is unchanged — the URL path emits the exact { url } connection object the old code inlined (pinned by a unit test). One deliberate change: a container started with no connection config now fails fast with Set REDIS_URL (single instance) or REDIS_SENTINELS + REDIS_SENTINEL_NAME (Sentinel) instead of the old { url: undefined }, which made ioredis silently dial localhost:6379 inside the container.

Docs updated: standalone README env table + Sentinel example, and the standalone-docker docs page.

Verification

• 9 unit tests (connection.test.ts): sentinel parsing (defaults, malformed entries), mode precedence, required-name validation, auth/db passthrough, and the exact URL-mode output shape.
• Ran the built bundle against a plain Redis via REDIS_URL: healthcheck and /api/queues serve live counts — single-instance behavior unchanged.
• Verified the fail-fast error on a container with no connection config.
• tsc --noEmit, bun build, and biome all pass.

Heads-up for reviewers: I did not run a live Sentinel failover topology against the built image — sentinel mode is verified at the config-shape level (the options object handed to BullMQ is standard ioredis sentinels/name config). Happy to add a compose-based sentinel smoke test if you'd like one in-repo.

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