* docs(manual): add introduction page
* docs(manual): rewrite getting started as guided first run
* docs(manual): rewrite writing specs as a folio tutorial
* docs(manual): document missing spec API in reference
* docs(manual): plain-language rewrite of runs page
* docs: real introductions on index pages and README
* fix(docs): sibling links from directory-style pages need ../
* fix(docs): correct sampling and restart-cost claims to match implementation
* docs: nav lists Introduction and Case study; roadmap points to milestone
* docs(manual): make getting started target the reader's own app, not Folio
* docs(manual): add Folio case study page
* docs: point manual navigation at the case study
* docs(readme): lead with the case study, fix roadmap link
* docs: roadmap links to milestone, sync clear-data default and cross-links
pj