docs: establish plugin documentation and development workflows

[Scaxlibur]

Summary

• reorganize repository and package documentation around landing pages, current reference, evidence, and historical material
• add a generated plugin catalog, deterministic documentation audit, tests, and documentation CI
• add the repo-local wavebench-plugin-development Skill with progressive references for development, packaging, conformance, and hardware evidence
• define the manual-first instrument-driver workflow, including mandatory Identity, Core-gap handoff, manual-backed evidence, independent package versions, and the main release boundary

Validation

• python scripts/generate_plugin_catalog.py --check
• python scripts/audit_docs.py — 180 Markdown paths, 0 errors, 0 warnings
• .venv/bin/python -m pytest -q tests/test_docs_audit.py tests/test_plugin_catalog.py — 14 passed
• python3 .agents/skills/wavebench-plugin-development/scripts/validate_skill.py --strict-git
• prior full repository validation on this branch — 1888 passed, 3 skipped

No plugin production wheel changed in the Skill-only final commit, so no plugin package version was bumped.