docs: compress README public face + add GitHub hygiene files

[ramen-implementer]

Summary

Public-face polish from a landing-page review: sharpens the 30-second visitor
funnel and adds the GitHub-native contribution surface the repo was missing.
Docs-only — the foundry job is path-scoped and will skip; this PR merges
on org-governance + merge-gate.

README compression

• Opening identity → "an evidence-gated OS lab for agent-native computing" (was "Rust OS experiment"; leads with the testable, evidence-gated nature instead of the language).
• New "The Short Version" block after the disclaimer — the compressed bet.
• Smoke proof promoted to its own "Try the Smallest Proof" section.
• "Useful help right now" — three tracks (serious systems / newcomer / docs).
• New secondary "Governance and Research" section (RamenOrg + research, kept parallel, no authority of their own).

New GitHub hygiene files

• SECURITY.md — private vulnerability reporting, "not production," posture pointers.
• CODE_OF_CONDUCT.md — Contributor Covenant 2.1.
• .github/PULL_REQUEST_TEMPLATE.md — evidence level, claim-boundary checklist, separation of duties.
• .github/ISSUE_TEMPLATE/{bug_report,hardware_evidence_report,docs_confusion}.md — the hardware-evidence template captures claim_path, appliance id, and provenance flags.

Not in this PR

• Screenshot / asciinema of the boot transcript — needs a recorded session; deferred. The textual "Try the Smallest Proof" block is the hook for now.

Validation

• git diff --check — clean.
• just foundry-org-governance-g0 — PASS (status_drift + all 19 metrics).
• No .rs / .toml / .idl / rust-toolchain changes → foundry skips on CI.

Separation of duties

Opened by ramen-implementer[bot] (A2); awaits approval + merge by a different
identity (A3).

[maxwellsantoro]

A3 approval (human, distinct from A2 author app/ramen-implementer). Docs-only public-face polish: README compression (OS-lab identity, Short Version, Try the Smallest Proof, Useful help now, Governance & Research) + 6 GitHub hygiene files (SECURITY.md, CODE_OF_CONDUCT.md, issue/PR templates). Validated: just foundry-org-governance-g0 PASS, git diff --check clean; foundry skipped on CI as docs-only. Separation of duties holds.