Enhance chapter content and metadata: Update SKILL.md to include requirements for chart axes in all widgets. Implement axis labels, arrowheads, and graduations in the simultaneous graph explorer widget. Update math curriculum JSON to reflect the status change of multiple chapters to live. Add last modified timestamps to chapter templates and generate corresponding metadata for improved site navigation and SEO.

.agents/skills/ofb/SKILL.md

@@ -50,6 +50,7 @@ bun run build       # production: JS + Zola + pagefind → public/
 | Chapter URLs | `/{subjectId}/{chapter-slug}/` (e.g. `/math/quadratic-equations/`) |
 | Map | Mermaid DAG view (`?view=tree`) driven by `graph.edges` |
 | Graph | `graph.edges` must be **acyclic**; builder throws on cycles |
+| Chart axes (all widgets) | Every coordinate chart must render **x/y axis labels, positive-direction arrowheads, and visible graduations (ticks + scale labels)**. Apply this consistently across all subjects/widgets. |
 | Accessibility | Avoid decorative characters that may render as emoji on mobile. Prefer broadly supported symbols/text so desktop and mobile stay visually consistent. |
 
 ## Common tasks → where to edit
@@ -130,6 +131,8 @@ Live chapters live under `content/{subject}/{slug}/`:
 
 **Checkpoints (all subjects):** use `book-question`, `book-question__prompt`, `book-question__solution` (styled in theme `_book.scss`). Never use `book-question__answer`.
 
+**Charts (all subjects):** coordinate charts in chapter widgets must include axis labels, arrowheads, and graduation/tick scale by default. Do not ship unlabeled axes.
+
 **Math checkpoints / dots:** follow [math-chapter-patterns.md](math-chapter-patterns.md); shared dot classes in `content/math/subject.scss`.
 
 Reference: `content/math/quadratic-equations/`.