feat: bind reference knowledge to agents

[SaladDay]

Agents can now use named reference documents as a knowledge capability. Create or upload Markdown/TXT documents, bind them to an Agent, and choose the latest or a fixed version. Current documents are included on each run across Claude Code, Codex, OpenCode and Pi, including resumed conversations. Existing conversation history is retained.

This reuses capability versions, workspace permissions and marketplace lifecycle. Each knowledge base allows 16 UTF-8 documents / 32 KiB; combined serialized references are bounded at 64 KiB. Unpublished knowledge does not expose new private revisions to other workspaces. Claude Code startup logs omit argument contents. Scope excludes RAG, embeddings, remote fetching, filesystem paths and rich-document conversion.

Validation:

• make check; native tests for all four adapters.
• Isolated PostgreSQL tests for creation, permissions, binding, updates, unbinding and unpublished version isolation.
• Real-browser creation, Markdown/TXT upload, delayed version loading, draft preservation, version switching and Chinese/English layouts.
• Independent blind review; findings addressed and affected checks rerun.