chore: set up GitNexus MCP

[dporkka]

Summary

Sets up GitNexus as a project-scoped code-intelligence MCP for Dev Plane.

• adds pinned GitNexus 1.6.12 MCP config for Codex
• adds project MCP config for Claude-compatible clients
• ignores the local .gitnexus/ graph/index database

Validation

• GitNexus 1.6.12 indexed Dev Plane successfully under Node 22 LTS
• index: 8,319 nodes / 21,104 edges / 305 clusters / 426 flows
• detect-changes --scope compare --base-ref main reports the diff touches only configuration files and no indexed symbols/processes
• git diff --check main...HEAD passes
• MCP startup smoke test stayed healthy until intentionally terminated by timeout

Runtime note

GitNexus 1.6.12's analyzer worker crashed under Node 24 in the isolated validation environment and succeeded under Node 22 LTS, so Node 22 is the tested runtime for indexing.

[chatgpt-codex-connector]

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