chore: pin toolchain and add type checking

- Pin TypeScript as a direct dependency. It was only present transitively
  via typescript-eslint, so nothing enforced tsconfig.json and nine
  latent type errors had gone unnoticed.
- Add `pnpm typecheck` (`tsc --noEmit`) and document it.
- Add .npmrc with engine-strict, so the declared Node and pnpm ranges
  are actually enforced.
- Ignore doc_build/ in ESLint. It was unignored and reported 1650 errors
  from build output, which made lint unusable as a gate.
- Refresh README, CLAUDE.md, AGENTS.md and CONTRIBUTING.md to match the
  current structure, build targets and navigation rules.

CLAUDE.md

@@ -6,21 +6,55 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 ```bash
 pnpm dev        # Start dev server with HMR
-pnpm build      # Production build (outputs to dist/)
+pnpm build      # Production build for .com (outputs to doc_build/)
+pnpm build:com  # Explicit .com build
+pnpm build:cn   # Production build for .cn
 pnpm preview    # Preview the production build locally
 pnpm lint       # ESLint (flat config)
+pnpm typecheck  # TypeScript, no emit
 pnpm format     # Prettier — format all files
 ```
 
+## Build targets
+
+`rspress.config.ts` exports a `createConfig(target)` factory; `rspress.cn.config.ts`
+is a three-line wrapper calling it with `"cn"`, passed via `--config`. The two
+targets differ in the canonical origin used for `head`, the sitemap and
+`robots.txt`, and in which social links are rendered. Both write to `doc_build/`,
+so build and deploy one target at a time.
+
 ## Architecture
 
-- **Rspress** static site (like VitePress but Rust-based toolchain). Documentation site generated from MDX/markdown files.
-- **Content root**: `docs/` — all documentation pages live here. Configured as `root` in `rspress.config.ts`.
-- **Navigation**: `docs/_nav.json` defines the top-level nav. Sidebar ordering is controlled by `_meta.json` files within subdirectories.
+- **Rspress v2** static site (like VitePress but Rust-based toolchain). Site generated from MDX/markdown files.
+- **Content root**: `docs/` — all pages live here, split into mirrored `en-gb/` and `zh-hans/` trees. Configured as `root` in `rspress.config.ts`.
+- **Navigation**: `docs/<locale>/_nav.json` defines the top-level nav; `text` values are i18n keys resolved through the root `i18n.json`, which is why both locale copies are identical. Sidebar grouping and ordering are controlled by `_meta.json` files within subdirectories.
 - **Custom theme**: `theme/index.tsx` re-exports everything from `@rspress/core/theme-original` and imports `index.css`. To customize any default theme component, import it and export it back — this is the standard Rspress theme override mechanism.
-- **CSS**: `theme/index.css` overrides CSS custom properties (`--rp-c-brand`, `--rp-c-brand-dark`, `--rp-c-brand-tint`) to set brand colors.
+- **CSS**: `theme/index.css` overrides CSS custom properties (`--rp-c-brand`, `--rp-c-brand-dark`, `--rp-c-brand-tint`) to set brand colours.
 - **MDX**: Content pages use `.mdx` when embedding React components, `.md` for plain Markdown. MDX type-checking is enabled via `tsconfig.json` `mdx.checkMdx`.
-- **pnpm** is the package manager (see `pnpm-lock.yaml`).
+- **pnpm** is the package manager, pinned via `packageManager` in `package.json` (see `pnpm-lock.yaml`).
+
+## Rspress gotchas
+
+- **Never add `_meta.json` beside `_nav.json`** at the root of a locale directory.
+  With both present, Rspress emits a single flat sidebar and silently discards
+  every per-section one.
+- **Never set `themeConfig.nav` or `themeConfig.sidebar`** in
+  `rspress.config.ts`. Either one switches off auto-generation and makes all
+  `_nav.json` / `_meta.json` files inert.
+- **Never set `themeConfig.footer`**. The site footer is the `SiteFooter`
+  component wired through the `Layout` `bottom` slot; setting `footer.message`
+  renders the built-in `HomeFooter` as well, on the home page only.
+- Entries in the site-level `head` array are **not** de-duplicated against the
+  theme's own meta tags. `og:title`, `og:description`, `description` and
+  `og:type` are already emitted from page metadata — do not repeat them there.
+- A `_meta.json` that omits a page drops it from the sidebar with no warning.
+- Dead markdown links fail the production build, but links in `_nav.json`,
+  `_meta.json`, `hero.actions` and React components do not.
+
+## Conventions
+
+- British English throughout — interface text, documentation, code comments and
+  commit messages.
 
 ## Rules