docs: README audit (tone, related repos)

[SuperInstance]

README audit per the standing checklist. Note: aider was dispatched first but correctly stopped and asked for clarification on all three checks rather than proceeding without the sibling-repo file/branch context it needs in non-interactive mode — it made zero edits (confirmed via git diff), so I completed the audit directly.

• Up to date: already accurate — the VM RAM spec (8-128GB) already reflects round 3's earlier fact-check fix, no new changes needed.
• Inter-connective: added a Related Repos section — plato-edge, nexus-edge-runtime, edge-relay-agent — all verified to exist via gh repo view and genuinely related (this repo's cloud-to-edge deployment research questions have working counterparts in each).
• Tone: softened one real overclaim ("unlimited bandwidth"/"cloud has unlimited resources" — cloud codespaces have real, if generous, bandwidth and cost limits) to accurate language, without touching the repo's existing honesty markers (✅/Researched column) which were already good.