Company Brain plugin canary and operator docs

[100yenadmin]

Upstream epic: electricsheephq/electric-sheep#2029
Related: #24, #25, #26

Summary

Add a plugin-side validation and operator documentation slice for the Company Brain company_brain_* tools. This keeps #26 focused on implementation while making the install/test path clear enough for pilots.

Scope

• Add a smoke/canary command or documented test path for company_brain_accounts_list, account brief, account timeline, and narrow query tools.
• Use Cortex contract fixtures from electricsheephq/electric-sheep#2033 when available.
• Validate that insufficient_evidence is treated as a successful honest response.
• Validate that source citations and action-readiness fields are preserved in tool output.
• Document operator/agent behavior around account resolution, source-backed context injection, GBrain/shadow non-authoritative context, and approval-gated action candidates.

Acceptance Criteria

• A maintainer can install/run the plugin canary against local or staged Cortex Company Brain endpoints.
• The canary catches schema drift before dashboard/runtime smoke testing.
• Docs explain the boundary between Company Brain injection mode #24 injection mode, Action-safety bridge for Company Brain context #25 action safety, and Company Brain MCP tools for account resolution and evidence-backed briefings #26 concrete tools.
• The plugin participates in the cross-repo smoke tracked by electricsheephq/electric-sheep#2034.

Non-Goals

• No generic always-on Company Brain injection.
• No outbound action execution.
• No dashboard UI implementation.

[100yenadmin]

Implemented by #28.

Landed the plugin Company Brain canary and operator docs covering insufficient_evidence, citations, action-readiness metadata, and the explicit tool boundary for the cross-repo smoke.