Add ugraph knowledge graph CLI

[shadow-enthusiast]

Summary

• add an agent-friendly ugraph Node CLI for querying .understand-anything/knowledge-graph.json without loading the whole graph into context
• support overview, find, node, neighbors, impact, context, layers, tour, and stale commands with compact JSON by default plus text/markdown formats
• expose the CLI through package bin, pnpm script, macOS/Linux installer symlink, and Windows .cmd shim
• document common agent workflows and add CLI coverage tests

Verification

• pnpm exec eslint understand-anything-plugin/bin/ugraph.js tests/ugraph.test.mjs
• pnpm exec vitest run tests/ugraph.test.mjs
• pnpm test
• pnpm build
• bash -n install.sh

Note: PowerShell syntax parsing was not run locally because pwsh is not installed in this environment.