docs update with case study (#63)

* 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

docs/manual/replay.md

@@ -22,7 +22,7 @@ The positional argument can be a runs directory or a single run directory (auto-
 | ActionList | Ordered list of steps with the verb and target for each action. |
 | Timeline | Per-property lane chart over the run; cells coloured by violated, pending, or holds. |
 | ViolationsPanel | Property statuses at the focused step with residual formulas for any that failed. |
-| HierarchyPanel | Filterable table of every UI element captured at the focused step; mirrors the selectors documented in [Spec language reference](./spec-language/). |
+| HierarchyPanel | Filterable table of every UI element captured at the focused step; mirrors the selectors documented in [Spec language reference](../spec-language/). |
 | SnapshotTable | Flattened `snapshots` map for the focused step, with diffs against the previous step. |
 | MetricsChart | Heap and other host-side metrics sampled per step. |
 | ExceptionsPanel | Uncaught exceptions captured during the run, with a jump-to-first control. |