MCP Track B Phase B3: expose initial read-only personal SimpleChat MCP tools

[Bionic711]

Summary

Implement the initial read-only personal-scope inbound SimpleChat MCP tools from #1013 after the inbound auth/governance foundation is in place.

Initial Tool Set

• show_user_profile
• list_conversations
• get_conversation_messages
• list_personal_documents
• list_personal_prompts
• search_personal_documents
• list_agent_template_tags

Scope

• Reuse existing SimpleChat authorization helpers and service functions where possible.
• Return minimized profile data; do not return raw token claims by default.
• Ensure conversation and message access is limited to the delegated user or valid collaboration access.
• Ensure personal documents/prompts are limited to the delegated user's personal workspace.
• Restrict search to personal documents only.
• Require pagination and maximum result limits.
• Respect the agent template gallery feature flag for list_agent_template_tags.
• Add audit logging per tool call without logging secrets or sensitive document/message content.

Acceptance Criteria

• Each initial tool is explicit in the inbound MCP registry.
• Each tool checks inbound MCP auth and governance before execution.
• show_user_profile returns minimized profile data.
• list_conversations returns only visible conversations for the delegated user.
• get_conversation_messages rejects inaccessible conversations.
• list_personal_documents returns only the delegated user's personal documents.
• list_personal_prompts returns only the delegated user's personal prompts.
• search_personal_documents enforces personal scope and bounded top_n.
• list_agent_template_tags respects the agent template gallery feature flag.
• Tests cover positive and negative access paths for every tool.

Notes

Parent: #1013
Depends on the inbound auth/governance foundation issue.
Planning doc: docs/explanation/features/MCP_PLUGIN_ROBUSTNESS_PLAN.md
Priority: P1
Size: L