docs: bring repo to estate documentation + contributor convention + substantial wiki

[hyperpolymath]

Summary

Brings julia-professional-registry to the same documentation completeness as hyperpolymath/hypatia, hyperpolymath/standards, and the rest of the well-organised estate. Pairs with PR #17 (the CI hygiene canary) to leave the repo in a "ready to merge to main, single-main reconciled" state.

What changed

Top-level docs (Phase 1)

• + CHANGELOG.md — Keep-a-Changelog format with [Unreleased] capturing the work of PR fix(ci): close 7 real code-scanning alerts (canary for estate sweep) #17 and this PR + a backfilled [1.0.0] for the 2026-04-04 CRG-C release; points at the standards changelog-reusable.yml for future auto-generation.
• + ROADMAP.adoc — vision, near/medium/long-term sections, non-goals, tracking.
• + MAINTAINERS.adoc — current maintainer table + responsibilities + nomination hook.
• + GOVERNANCE.adoc — BDFL model adapted to registry context (package-registration decision hierarchy added on top of the hypatia template).
• - CONTRIBUTING.adoc — removed; was duplicate of CONTRIBUTING.md in a second format.
• **~ CONTRIBUTING.md** — corrected the dev-env line from nix develop to guix shell -D -f guix.scm per standards#101; added a "Registering a Package" section.

.github/ template fleet (Phase 2)

• + .github/CODEOWNERS — default @hyperpolymath + per-area assignments for Registry.toml, workflows, machine-readable, security.
• + .github/FUNDING.yml — sponsor button.
• + .github/pull_request_template.md — RSR checklist + registry-specific subsection (Registry.toml + per-package TOML consistency + upstream quality bar).
• + .github/copilot-instructions.md — estate banned-languages + registry directory shape + SHA-pin requirement for wrapper workflows.
• + .github/ISSUE_TEMPLATE/bug_report.md — registry-tailored (Pkg-aware repro, package-row reference).
• + .github/ISSUE_TEMPLATE/feature_request.md — with an estate-alignment field so drift away from standards is surfaced.
• + .github/ISSUE_TEMPLATE/package_registration.md — new template; registration is the most common kind of issue this repo sees, and a structured template enforces the quality-bar checklist from GOVERNANCE.adoc.

Wiki (Phase 3, pushed to julia-professional-registry.wiki)

Replaced the placeholder "Welcome to the wiki" with nine substantive pages plus a sidebar:

• Home — landing page with quick links and at-a-glance table
• Registry-Usage — Pkg.Registry.add, install, update, remove, troubleshooting
• Packages — full table of 34 registered packages with descriptions + on-disk layout + cross-references
• Registering-a-Package — quality bar + step-by-step (directory structure → Registry.toml → PR title convention → review flow), plus yank/update guidance
• Architecture — full repo module map, component roles, workflow table, "what this is not"
• Testing — CRG-C grade context, what is/isn't tested at the registry level, local-run instructions, CI gates, path toward Grade B
• Governance — BDFL summary, role table, decision flow, becoming-a-maintainer
• Roadmap — near/medium/long-term + non-goals + how to influence
• Security — reporting, response timeline, safe harbour, code-scanning posture, self-echo note pointing at hypatia#368
• _Sidebar — wiki nav grouped by Getting-Started / Maintainers / Project / External

Every wiki page links back to the canonical file in main and is explicit that the file wins on disagreement.

Why now

You asked: "is everything fully documented for humans and machines, everything cleaned up and organised, with the wiki complete and substantial, and is there anything that needs updating in the dot files or elsewhere before it can be merged to the main branch, and the other branches reconciled similarly to leave that single main?"

This PR + PR #17 are the answer for the docs/dotfiles/wiki axes. PR #16 reconciliation is the remaining piece; tracked separately.

Test plan

• CI green
• Wiki renders cleanly on github.com/hyperpolymath/julia-professional-registry/wiki
• No regression in PR fix(ci): close 7 real code-scanning alerts (canary for estate sweep) #17's checks (the two PRs touch disjoint files; should be conflict-free)

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