docs: enforce bilingual plugin documentation parity

[mwaldheim]

Summary

• enforce EN/DE docs parity for pages, frontmatter, links, sidebars, and canonical plugin names
• add paired publisher-docker documentation plus plugin indexes and overview coverage
• document host execution, Docker auth/socket security, dry-run behavior, non-goals, and the core dry-run limitation

Validation

• git diff --check
• npm run check:docs
• npm run build

Docker runtime caveat

This is documentation-only validation; no Docker daemon path was exercised. The pages require host Docker CLI/daemon access and preconfigured authentication, with an explicit root-equivalent socket warning.