Improve graph communities and add memory demo

[Coding-Dev-Tools]

Summary

• add a privacy-safe direct-memory-link fallback for entity-free A-MEM graphs, with bounded SQL projections and regression coverage
• make community-island layout deterministic while keeping cross-community influence bridges visible and preserving the complete graph explorer dataset
• add a reproducible local screen-demo source and recorder while gitignoring all generated payloads, frames, WebM files, and the final MP4
• make Playwright launch the checked-out dashboard instead of a stale globally installed entry point

Local verification

• python -m pytest tests/ -q
• ruff check .
• npx playwright test (4 passed)
• node --check engraphis/static/dashboard.js
• node --check demo/record_screen_demo.mjs
• sample and CodeMem retrieval evals: recall@5, hit@5, token recall all 1.0
• ablation: base vector/1-hop/PPR 1.0; multi-hop PPR 1.0
• package build and twine check dist/*
• 57.08-second 1920x1080 H.264 demo recording generated and visually sampled locally; output remains ignored

Merge gate

Local Docker is unavailable, so merge is gated on both normal PR CI and a non-publishing manual release.yml run for this branch. That workflow performs the clean dependency audit, Python matrix, browser checks, package checks, and production Docker health smoke. No tag or package publication is requested by this PR.

[chatgpt-codex-connector]

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