XY-1059: [ELF AMK P0] Codify product contract, roadmap, and phase-gate execution plan

[yvette-carlisle]

Summary

• Add the durable ELF Agent Memory + Knowledge System product contract and P0-P5 roadmap.
• Route the new contract through docs indexes, the docs log, and the version registry.
• Add a checks cargo-make alias so the registered workflow verification command resolves through repo task authority.

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make checks (322 passed, 87 skipped)

Review

• Independent fresh-context read-only review checkpoint recorded clean for ca2da6f7a6cec69286a3801b907353d956172c52.