[Bot] Add Jetstream support

[zoedsoupe]

Add support for the simpler Jetstream format for event streaming in bots as an alternative to the binary CBOR-based firehose.

Implementation tasks:

• Create ProtoRune.Bot.Jetstream module
• Add WebSocket connection to Jetstream endpoints
• Implement JSON message parsing and normalization
• Convert Jetstream events to the same format used by existing strategies
• Support filtering by collection or repo

Reference: See recent Jetstream announcement and review the existing polling implementation in lib/proto_rune/bot/poller.ex.