docs: restructure public product documentation

[reiase]

Summary

• restructure the public documentation around the two product entry points, pVisor and pChronicle
• keep the current execution-to-history architecture while removing pPilot from the public overview and diagram
• rewrite the pVisor CLI design page around Run startup, review/apply/drop, checkpoints, environments, and configuration precedence
• add the pVisor case catalog to the English and Chinese documentation navigation
• replace the landing page with a formal product overview, architecture section, operating principles, and documentation paths

Validation

• just docs-build
• just docs-links
• just docs-i18n
• git diff --check
• SVG XML validation with xmllint