Add Zola skill documentation and Solid.js reference; update spec.md with i18n note

.agents/skills/zola/SKILL.md

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+---
+name: zola
+description: >-
+  Build and maintain the Open Free Books static site with Zola (Tera templates,
+  Sass, content/, data/, theme) and Solid.js frontend. Use when editing zola.toml,
+  content/, themes/openfreebooks/templates/, Sass, static assets, frontend/src/,
+  bundle.js, or running zola build/serve.
+---
+
+# Zola (Open Free Books)
+
+Static site: **Zola** + custom theme `openfreebooks`. Output goes to `public/` (gitignored). Deploy via Wrangler from `public/`.
+
+## Layout
+
+| Path | Role |
+|------|------|
+| `zola.toml` | Site config, `[extra]` URLs for templates |
+| `content/` | Pages (`*.md` + front matter, `template = "…"`) |
+| `data/` | JSON for `load_data()` (contributors, credits) |
+| `static/` | Copied to site root (`favicons`, `icons/`, etc.) |
+| `themes/openfreebooks/templates/` | Tera HTML, partials, macros |
+| `themes/openfreebooks/sass/` | Source styles → compiled `public/main.css` |
+| `themes/openfreebooks/static/` | **Only** committed build artifact: `js/bundle.js` |
+
+See [reference.md](reference.md) for Tera pitfalls and build checks.
+
+## Commands
+
+```bash
+bun run build:js   # Vite → themes/openfreebooks/static/js/bundle.js
+zola serve         # dev at http://127.0.0.1:1111
+bun run build      # build:js + zola build → public/
+```
+
+After Sass or template changes, run `zola build` (or `zola serve`). Do **not** copy `public/` into `themes/openfreebooks/static/`.
+
+## Templates (Tera)
+
+- Extend `base.html`; use `{% block content %}` for page bodies.
+- **`{% import "macros/….html" as ns %}`** only in templates that **extend** a layout (e.g. `index.html`), **not** inside `{% include %}` partials.
+- Macro calls use **keyword arguments**: `{{ ns::macro_name(arg=value) }}`.
+- Prefer **partials** under `templates/partials/`; kebab-case filenames.
+- Icons: Tabler SVGs in `static/icons/social/`; inline copies in `templates/partials/icons/social/*.html` included from `macros/social-icons.html`.
+
+## Data files
+
+```tera
+{% set data = load_data(path="data/contributors.json", format="json") %}
+```
+
+On Zola 0.22+, use the `data/…` path (not bare `contributors.json` at repo root).
+
+## New page checklist
+
+1. Add `content/your-page.md` with `title`, `template = "your-template.html"`.
+2. Add `themes/openfreebooks/templates/your-template.html` extending `base.html`.
+3. Add Sass in `themes/openfreebooks/sass/` and `@import` in `main.scss`.
+4. Wire footer/nav URLs in `zola.toml` `[extra]` if needed.
+
+## Styling
+
+- No inline Tailwind; use Sass partials and `class=""` on elements.
+- Design tokens in `_tokens.scss`; section patterns in `_components.scss`, `_why-sections.scss`, etc.
+- Grain overlay and dark mode via `data-theme` + CSS variables.
+
+## Solid.js
+
+Client behavior (header, marquee, scroll reveal, dialogs, theme toggle) lives in `frontend/` and mounts from `base.html` via `js/bundle.js`.
+
+**When changing `frontend/` or adding interactivity**, read [zola-solid.md](zola-solid.md) before editing JS.
+
+## Verify
+
+```bash
+bun run build
+```
+
+Confirm `public/main.css` contains new selectors (no stale `themes/openfreebooks/static/main.css` overriding compile). Confirm HTML under `public/` matches templates, not an old `themes/openfreebooks/static/index.html`.