[codex] Prepare public OSS candidate surface

[Mushkrot]

Summary

This PR prepares Recallant's public repository surface for Codex for OSS review while keeping the active public history intact.

It moves the current public tree toward a reviewer-friendly OSS shape: product-facing docs, contributor guidance, security posture, quickstart/self-hosting material, roadmap, comparison notes, and issue/PR templates.

What changed

• Rewrote the top-level README to explain what Recallant is, why AI developers and OSS maintainers need governed memory, and how to prove the capture/recall loop.
• Replaced the owner/internal AGENTS.md with a public AI-agent and contributor guide.
• Kept only curated public docs in docs/: quickstart, self-hosting, client setup, architecture, security, why Recallant, comparison, roadmap, and docs index.
• Removed internal planning material from the current public tree: stage goals, handoffs, dated audits, ADR history, owner-server notes, project log, and implementation-only docs.
• Added CONTRIBUTING.md, CODE_OF_CONDUCT.md, GitHub issue templates, and a PR template.
• Updated public-readiness and public-security smoke scripts for the cleaned public surface.

Why

The goal is to make Recallant understandable to both human reviewers and AI-review agents without exposing internal working notes as the first thing they see. The repository should present the product, its motivation, proof path, security model, and roadmap clearly while the internal development archive remains outside the public surface.

Validation

Passed locally before this branch was published:

• npm run public-readiness:smoke
• npm run public-security:smoke
• npm run format:check
• npm run lint
• npm run build

Notes

This PR is intentionally a documentation and public-surface cleanup. It does not claim the full product is complete; the docs describe Recallant as pre-release and focus on the first production-ready coding-agent memory slice.