[DO NOT MERGE] Add MegaMoE engineering skill

[GwilliamHu]

Important

Personal reference PR for agent reuse. Please do not merge.

Motivation

Preserve the MegaMoE architecture, validation, debugging, performance-tuning,
environment, and historical-evidence knowledge needed to work safely across
FlyDSL, AITER, MORI, ATOM, SGLang, and the customer FlyDSL_universe branch.

Technical Details

• Add a progressively disclosed megamoe-engineering skill with task-based
  routing to focused references.
• Capture protocol invariants for fixed/compact dispatch, quant/prepare,
  Stage1/Stage2, fanout/dedup, readiness, AOT/preload, CUDA Graph, and capacity.
• Add trace-led tuning and root-cause workflows, 8-GPU/AOT/serving validation
  gates, model geometry/onboarding guidance, and a dated evidence index.
• Add a read-only preflight helper that reports source/runtime/GPU ownership
  provenance without initializing the GPU runtime.
• Link the skill from CLAUDE.md for repository-local discovery.

Test Plan

• Run the repository agent-document/API checks.
• Run the skill validator.
• Syntax-check and execute the read-only preflight helper.

Test Result

• python3 scripts/check_repo.py: PASS
• python3 scripts/check_docs_api.py --all: PASS
• quick_validate.py .claude/skills/megamoe-engineering: PASS
• bash -n .../scripts/preflight.sh: PASS
• Preflight end-to-end smoke: PASS