Add Reader Bridge capture contract

[mdheller]

Summary

Adds a contract-only BearBrowser Reader Bridge for the canonical SocioProphet Feed Intelligence reader in SocioProphet/socioprophet/socioprophet-web/client-vue.

What changed

• Defines BearBrowser as capture and provenance surface, not the reader UI.
• Defines browser reader bridge event classes.
• Defines a minimal ReaderHandoff payload.
• Preserves downstream boundaries: SlashTopics resolves governance scope, New Hope evaluates membrane admission, MemoryMesh handles scoped recall and review-only writeback posture, MeshRush handles graph views, and ActivityPub publication is not implied by browser capture.

Validation notes

Connector inspection confirms the PR is open, mergeable, and changes one docs file: docs/reader-bridge.md.

Non-goals

• No runtime code.
• No feed fetching implementation.
• No publication behavior.
• No MemoryMesh writeback.
• No MeshRush traversal.
• No ActivityPub action.