[EPIC] Project Rosetta - modern docs, support tiers, roadmap and governance

[k5602]

Goal

Overhaul MetaCall documentation and governance. Make docs correct, complete, and maintainable. Add clear support tiers for OS, language, port, and loader. Add roadmap and security policy. Improve contributor and agent guides.

Why

Docs live in one large file docs/README.md (~1212 lines). Many sections are empty. Version tables list EOL runtimes. Loader and port tables miss real targets and list future targets that already exist. Governance files are missing at root. Contributors and agents lack clear build and test rules and even project aim or future tasks.

Scope

• Restructure docs/ with Diataxis layout and docs-as-code checks.
• Refresh reference content for core, reflect, loaders, ports, serials, detours, CLI.
• Define Tier 1, 2, 3 for OS x arch x loader x port.
• Update all runtime version data and platform tables.
• Add ROADMAP.md and SECURITY.md.
• Improve CONTRIBUTING.md, CODE_OF_CONDUCT.md, SUPPORT.md, AGENTS.md.
• Modernize C, C++, Clang and toolchain baselines.
• Fix links, images, TOC, and install docs.

Non-goals

• No loader runtime upgrades in this epic. Track upgrades as separate issues per loader.

Success criteria

• New docs/ nav builds in CI with no broken links.
• Zero empty headings in main docs or explicit stubs with owners.
• Tier matrix published and linked from README.
• ROADMAP.md and SECURITY.md exist at root.
• CONTRIBUTING.md has full build, test, style flow.
• AGENTS.md stays short with nested guides per area.
• Toolchain baselines agreed and CI green.
• Maintainer approves each subissue before work starts.

Tracking list

• [Rosetta-0] Audit and freeze current docs and matrix #864 Rosetta-0: audit and freeze
• [Rosetta-1] New docs layout and stack with Diataxis #865 Rosetta-1: new layout and stack
• [Rosetta-2] Reference refresh for core, loaders, ports, serials, detours #866 Rosetta-2: reference refresh
• [Rosetta-3] OS-lang-port-loader support tiers Tier 1, 2, 3 #867 Rosetta-3: OS-lang-port-loader tiers
• [Rosetta-4] Version and platform data update #868 Rosetta-4: version and platform data update
• [Rosetta-5] Add ROADMAP.md #869 Rosetta-5: ROADMAP.md
• [Rosetta-6] Add SECURITY.md #870 Rosetta-6: SECURITY.md
• [Rosetta-7] Improve CONTRIBUTING, conduct, support #871 Rosetta-7: CONTRIBUTING, conduct, support
• [Rosetta-8] Split and tighten AGENTS.md #872 Rosetta-8: AGENTS.md split
• [Rosetta-9] Modernize C, C++, Clang and toolchains #873 Rosetta-9: Clang and toolchain modernization

References

• docs/README.md
• README.md
• source/loaders/CMakeLists.txt
• source/ports/CMakeLists.txt
• source/tests/CMakeLists.txt
• .github/CONTRIBUTING.md
• .github/CODE_OF_CONDUCT.md
• .github/PULL_REQUEST_TEMPLATE.md
• docs/api-docs/config/doxyfile.in
• docs/CREATING_A_LOADER.md
• TODO.md, VERSION, NOTICE, AUTHORS