feat(docs): vitepress site for docs/, mermaid rendering, ci build workflow

Implementation of ADR-0022.

* `vitepress`, `vitepress-plugin-mermaid` and `mermaid` added to
  workspace devDependencies. Build settled at ~9 s for the full
  site, sub-second incremental in dev.
* `docs/.vitepress/config.mts`:
  * `srcExclude` drops `docs/README.md` (git/IDE-only index) and
    `docs/decisions/template.md` (authoring scaffold).
  * `rewrites` maps `decisions/README.md` → `decisions/index.md`
    so `/decisions/` resolves to the curated landing while the
    source stays git-friendly.
  * `ignoreDeadLinks` skips cross-repo refs (`../CLAUDE`,
    `../../apps/**`, `../../notes/**`), `localhost:*` dev URLs,
    and the deliberately-excluded `README`/`template` references —
    the source stays usable from a git/IDE reader without
    breaking the site build.
  * Auto-generated sub-sidebar for `/decisions` walks
    `00NN-*.md` so adding an ADR is one file.
  * Mermaid via `withMermaid` with `securityLevel: 'strict'`.
* `docs/index.md` — VitePress Hero landing with four feature
  cards (Architecture, Decisions, Development, Onboarding).
* `package.json` exposes `docs:dev`, `docs:build`, `docs:preview`.
* `docs/development.md` (line ~5): `[setup/](setup/)` → first
  page, since folder-style links don't resolve cleanly under
  `cleanUrls`. Line 330: wrap `${{ github.* }}` in
  `<code v-pre>…</code>` so VitePress's Vue template parser
  doesn't trip on the curly-brace interpolation.
* `.gitea/workflows/docs-site.yml` — builds on every PR (gate
  on parse errors + genuine dead links), uploads the dist as an
  artifact on push to main. The Mermaid plugin regression fence
  greps for `class="mermaid"` / `<svg>` in ADR-0009's rendered
  HTML.
* `.gitignore` excludes `docs/.vitepress/{cache,dist}/`.

Deployment target stays provisional per ADR-0022; the workflow
publishes a `docs-site` artifact for now. The rsync step lands
once the future infrastructure ADR locks the host.

docs/.vitepress/config.mts

@@ -0,0 +1,164 @@
+import { readdirSync } from 'node:fs';
+import { join } from 'node:path';
+import { defineConfig } from 'vitepress';
+import { withMermaid } from 'vitepress-plugin-mermaid';
+
+/**
+ * VitePress configuration for the APF Portal documentation site
+ * per ADR-0022.
+ *
+ * Source tree maps directly to URLs:
+ *   docs/index.md                → /
+ *   docs/development.md          → /development
+ *   docs/architecture.md         → /architecture
+ *   docs/decisions/README.md     → /decisions/
+ *   docs/decisions/00NN-…md      → /decisions/00NN-…   (auto-listed sidebar)
+ *   docs/setup/0N-…md            → /setup/0N-…
+ *
+ * `docs/README.md` stays as the git-side / IDE-preview index and is
+ * therefore excluded from the published site; `decisions/template.md`
+ * is an authoring scaffold, also excluded.
+ */
+
+const DECISIONS_DIR = join(__dirname, '..', 'decisions');
+const ADR_FILE_RE = /^\d{4}-[\w-]+\.md$/;
+
+/**
+ * Walks `docs/decisions/` and returns one sidebar entry per accepted
+ * ADR (`NNNN-kebab-title.md`), ordered by numeric prefix. Adding a
+ * new ADR is then a single-file change — no `config.ts` edit
+ * required (the convention spelled out in ADR-0022 §"Sidebar
+ * generation").
+ *
+ * The link text drops the numeric prefix's leading zeroes to read
+ * naturally ("ADR-0009 — …") while the underlying URL keeps the
+ * full filename for stable routing across renames.
+ */
+function adrSidebarItems(): { text: string; link: string }[] {
+  return readdirSync(DECISIONS_DIR)
+    .filter((name) => ADR_FILE_RE.test(name))
+    .sort()
+    .map((name) => {
+      const slug = name.replace(/\.md$/, '');
+      const num = slug.slice(0, 4);
+      const title = slug.slice(5).replace(/-/g, ' ');
+      return {
+        text: `ADR-${num} — ${title}`,
+        link: `/decisions/${slug}`,
+      };
+    });
+}
+
+export default withMermaid(
+  defineConfig({
+    title: 'APF Portal Documentation',
+    description:
+      "Architecture decisions, development guide, and onboarding material for APF France Handicap's web portal.",
+
+    // Root files (`README.md`) and authoring artefacts (`template.md`)
+    // never make it to the rendered site — see ADR-0022.
+    srcExclude: ['README.md', 'decisions/template.md'],
+
+    // The curated decisions index lives in `decisions/README.md`
+    // (git/IDE convention). VitePress expects `index.md` at a
+    // folder root for clean URLs, so we rewrite at build time —
+    // source layout stays git-friendly, the published URL resolves
+    // `/decisions/` to the curated landing.
+    rewrites: {
+      'decisions/README.md': 'decisions/index.md',
+    },
+
+    // ADRs and the development guide carry deliberate references to
+    // files that live OUTSIDE `docs/` (CLAUDE.md, apps/**, infra/**,
+    // notes/**), localhost URLs that only resolve in a dev session,
+    // and the authoring `template.md` we explicitly excluded. All of
+    // those are valid from a git/IDE reader's perspective; VitePress
+    // is told to skip them rather than fail the build.
+    ignoreDeadLinks: [
+      /^https?:\/\/localhost/,
+      /^\.{1,2}\//,
+      /\/template$/,
+      /\/README$/,
+    ],
+
+    // VitePress emits `.html` files by default; clean URLs hide the
+    // extension. Mirrors what readers will see in the browser address
+    // bar and what the inline ADR refs in `portal-admin` already use
+    // when they target Gitea source-view (forward-compatible the day
+    // we flip those refs to point at the docs site).
+    cleanUrls: true,
+
+    // The site is internal + read-only; we let crawlers in by
+    // default but won't ship a sitemap until the hostname is locked
+    // by the future infra ADR.
+    lastUpdated: true,
+
+    themeConfig: {
+      nav: [
+        { text: 'Development', link: '/development' },
+        { text: 'Architecture', link: '/architecture' },
+        { text: 'Decisions', link: '/decisions/' },
+        { text: 'Onboarding', link: '/setup/01-wsl-terminal-setup' },
+      ],
+
+      sidebar: {
+        '/development': [
+          {
+            text: 'Daily development',
+            items: [{ text: 'Repo layout & commands', link: '/development' }],
+          },
+        ],
+        '/architecture': [
+          {
+            text: 'Architecture',
+            items: [{ text: 'C4 + module boundaries', link: '/architecture' }],
+          },
+        ],
+        '/decisions/': [
+          {
+            text: 'Decisions',
+            items: [
+              { text: 'Index by theme', link: '/decisions/' },
+              ...adrSidebarItems(),
+            ],
+          },
+        ],
+        '/setup/': [
+          {
+            text: 'Onboarding',
+            items: [
+              { text: 'WSL terminal setup', link: '/setup/01-wsl-terminal-setup' },
+              { text: 'Dev web stack', link: '/setup/02-dev-web-stack' },
+              { text: 'Angular + Nx monorepo', link: '/setup/03-angular-nx-monorepo' },
+            ],
+          },
+        ],
+      },
+
+      socialLinks: [
+        { icon: 'git', link: 'https://git.unespace.com/julien/apf_portal' },
+      ],
+
+      search: {
+        provider: 'local',
+      },
+
+      outline: {
+        level: [2, 3],
+      },
+
+      footer: {
+        message: 'APF Portal — internal documentation',
+      },
+    },
+
+    // `vitepress-plugin-mermaid` passes its `mermaid` key through to
+    // the Mermaid runtime. Theme `default` follows VitePress's
+    // light/dark switcher automatically; explicit `securityLevel`
+    // tightens the renderer so diagrams can't inject arbitrary HTML
+    // from the source markdown.
+    mermaid: {
+      securityLevel: 'strict',
+    },
+  }),
+);