docs(agentos): MemoryCore.md — extract operational/tooling reference to tooling docs; rewrite to compelling conceptual guide (bar)

Part of #14310. Refs #14310. Completes the quality bar that the de-stale pass (merged #14334, Resolves #14317) did not reach.

Problem. #14334 fixed the facts but left learn/agentos/MemoryCore.md a 355-line spec-dump: roughly half is internal tooling/reference — the full MCP Tools catalog, the Healthcheck Response Shape payload spec (including a migration-census changelog note), the Backup/Restore CLI flag tables (incl. --force-topology-mismatch), the Configuration file format, and runtime-primitive internals. Operator (2026-06-29): "does NOT meet my quality bar, not even close… internal tooling crap… not compelling to anyone." (My review approving #14334 missed this — I verified the opening, not the whole guide.)

The guide conflates two doc types: (1) the conceptual "what Memory Core is + why it's the moat" guide (the bar: compelling narrative, dual-audience), and (2) operational tooling reference. The latter belongs in the dedicated tooling docs that already exist.

Acceptance Criteria

• Extract the operational/reference sections to their existing homes — tooling/RestorationRunbook.md (backup/restore CLI + flags + safeguards), tooling/MemoryCoreMcpApi.md (the MCP tool catalog), tooling/MultiTenantMigrationGuide.md (migration census) — verifying each target already covers the content before deleting (no unique-info loss). Replace the inline dumps with a tight "Operations & reference" link section.
• Cut pure changelog / healthcheck-payload spec that is not conceptual (relocate any genuinely-useful bit).
• Rewrite what remains as a compelling end-to-end narrative arc (problem → why → how → what's in it for you), keeping the restored hippocampus / stigmergy / dual-audience spine. A guide that earns the read, not a reference manual.
• Every diagram + cross-link render-verified.

⚠️ V-B-A grounding: the merged MemoryCore.md (origin/dev) + the three tooling docs (confirm coverage) + the #14310 content rubric.

Files: learn/agentos/MemoryCore.md (+ the tooling docs if content must move, not just link).