Improve debugging

[jasonvarga]

Adds visibility into why the Collaboration addon's websocket isn't connecting. Previously, a misconfigured broadcast setup (wrong Pusher cluster, unreachable Reverb server, etc.) would leave the "Attempting websocket connection…" banner stuck with zero signal in the console or UI.

• Logs channel-level events: echo.join, channel.subscribed, channel.error.
• Logs pusher-js connection state transitions and errors (feature-gated on Echo.echo.connector.pusher.connection, so non-pusher-js drivers are unaffected).
• After 5 seconds of waiting, logs a "still waiting — is your broadcast server running and reachable?" hint, and swaps the status bar banner to "Taking longer than expected. Check the browser console for details." so non-devs get a signal to go look.
• Uses console.error for the error paths so they stand out.
• Extracts a small logger.js module (debug / error) so the [Collaboration] prefix lives in one place.