Add remote bridge primitives

[chubes4]

Summary

• Add generic remote bridge client registration and queue item value objects.
• Add a replaceable bridge store contract with an option-backed default and facade for register/enqueue/pending/ack.
• Keep Core Connectors API as optional connector metadata via connector_id/wp_get_connector() instead of duplicating connector settings.
• Document the queue-first bridge protocol separately from direct WP_Agent_Channel transports.

Closes #101.

Testing

• php tests/remote-bridge-smoke.php
• composer test
• homeboy lint --force-hot

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the implementation, smoke coverage, protocol docs, lint cleanup, and PR description; Chris remains responsible for review and merge.