[Bot] Implement Firehose strategy

[zoedsoupe]

Extend the Bot framework to support real-time event processing using the firehose event stream. The current Bot implementation only supports polling.

Implementation requirements:

• Create ProtoRune.Bot.Firehose module similar to existing Poller
• Implement WebSocket connection to the repo subscription endpoint
• Add binary CBOR decoding for event messages
• Process events using the same event dispatch mechanism as polling
• Support backfill using sequence numbers
• Implement reconnection handling with backoff strategy

Reference: See Event Stream specification for details on the wire format and backfill mechanism.