feat(protocol): document Blendmate protocol v0.1

[lebduska]

Goal:

• Create a top-level protocol document for Blendmate v0.1 that defines the message types, structure, versioning, and how events are formatted.

Definition of Done:

• A Markdown or JSON schema document docs/protocol-v0.1.md that includes:
  • Protocol version identifier
  • Message envelope structure (type, source, payload)
  • Links to event catalog (protocol-events-v0.1.json)
  • Examples of valid messages for key events.

How to test:

• Document should be human-readable and include at least 3 message examples.
• Must include versioning and backward compatibility notes.

Constraints:

• Keep it compatible with planned UI and addon event reporting.