Rewrite and condense documentation, fix factual errors
Condense most pages to concise reference format. Add Import.md.
Fix: history file is history.json not session.json, import uses
URL input not file picker, getVariable() returns null not undefined.
- Add Translation.md with simplified 3-step process for translators
- No build/test required - just download, translate, and submit
- Link from Home.md (Development section)
- Link from Contributing.md (new Translations section)
