BR-6: Simone-MCP as canonical WRITE/edit layer (keep, do not replace)

[Delqhi]

Plan: docs/plans/simone-edit-layer.md

Simone-MCP (Delqhi/Simone-MCP) is the surgical AST symbol-edit layer and the moat vs text-diff agents. It is NOT a weak tool to replace. This issue anchors it as the canonical WRITE layer and wires it into the stack.

Scope:

• Whitelist simone as 2nd canonical MCP server alongside sin in all 3 CLIs (sin mcp-config --with-simone)
• SCKG -> Simone symbol-index export (closes Simone v0.2.0 roadmap gap: repo-wide refactors)
• Mutating Simone call emits link_evidence event into SIN-Brain evidence graph
• AGENTS.md routing rule: all code changes via Simone symbol-tools, not raw text patches

Role separation: READ=SCKG, WRITE=Simone, REMEMBER=SIN-Brain, VERIFY=Oracle/POC.
Relates: BR-3 (mcp-config), BR-5 (Serena symbol-tools -> Simone), SIN-Brain SB-2 (evidence graph).