fix(streams): use event-based reconnection in mdns-ws provider

[dirkwa]

Summary

The mdns-ws WebSocket provider failed to reconnect when the remote server was temporarily unreachable (e.g. ENETUNREACH during a simultaneous reboot of both devices).

connectClient() relied on the one-shot Promise returned by client.connect(). When the initial connection failed, the Promise rejected and the .then() block — which sets up provider status, subscriptions, and remoteSelf context mapping — never executed. Even though the underlying @signalk/client Connection successfully reconnected later via its internal backOffAndReconnect() mechanism, the setup logic was skipped permanently.

The fix replaces the Promise-based pattern with persistent event listeners:

• client.on('connect') runs on every successful connection (initial + reconnections), ensuring subscriptions and provider status are always set up
• client.on('disconnect') updates provider status when the connection drops
• client.on('error') reports connection errors to the dashboard

Testing

Automated tests — 4 new integration tests in mdns-ws.test.ts using a real WebSocket server:

• Provider status set on successful connection
• Provider error set on connection failure (unreachable port)
• Disconnect detected when server closes
• Delta data flows through the stream with correct $source annotation

Manual tests against a live Signal K server (localhost:4000):

• Verified connect event fires on initial connection and updates provider status
• Verified socket kill triggers disconnect event, followed by automatic reconnection with a second connect event
• Verified connection to an unreachable port generates error events with exponential backoff retries (250ms → 500ms → 750ms → 1000ms), confirming the client keeps retrying until the remote becomes available

fixes #2513