feat(help): redesign help documentation

[helbertm]

Summary

• reorganize Help into an educational, topic-based guide with a sticky topic index and docked actions
• document supported SQLite file extensions, session persistence, updates, history, favorites, and SQL Map usage
• keep guidance synchronized across en-US, pt-BR, and es-ES
• preserve responsive behavior, keyboard focus, and accessibility semantics

Validation

• npm run validate:linux-metadata
• npm run validate:full:ci
• npm run validate:dependencies
• npm run quality:docker
• npm run quality:security:docker
• npm run validate:browser:quality (6 locale/viewport combinations, zero axe violations)
• npm run validate:native:chromium (Chrome 150, all locales, zero remote requests)

Impact

• no new network access
• no persistence or database behavior changes
• user-facing documentation and Help layout only