ci: add separate docs-check workflow for Markdown lint and Mermaid parse validation

- docs-check.yml runs on push/PR only when .md files change
- markdown-lint job: uses markdownlint-cli to check all .md files
- mermaid-parse job: extracts all mermaid blocks from .md files and
  validates each via mmdc (mermaid-js CLI) in headless Chromium
- Both jobs use continue-on-error: true so docs failures never block
  a release or fail the main CI pipeline
- .markdownlint.json disables MD013 (line length), MD033 (inline HTML),
  MD041 (first-line heading) to reduce noise on this repo

.gitea/workflows/docs-check.yml

@@ -0,0 +1,109 @@
+name: Docs Check
+
+on:
+  push:
+    branches: ["**"]
+    paths:
+      - "**.md"
+      - ".gitea/workflows/docs-check.yml"
+  pull_request:
+    branches: ["**"]
+    paths:
+      - "**.md"
+      - ".gitea/workflows/docs-check.yml"
+
+jobs:
+  markdown-lint:
+    name: Markdown lint
+    runs-on: ubuntu-latest
+    continue-on-error: true
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+
+      - name: Install markdownlint-cli
+        run: npm install -g markdownlint-cli
+
+      - name: Lint all Markdown files
+        run: markdownlint "**/*.md" --ignore node_modules
+
+  mermaid-parse:
+    name: Mermaid diagram parse check
+    runs-on: ubuntu-latest
+    continue-on-error: true
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+
+      - name: Install mermaid-js CLI
+        run: npm install -g @mermaid-js/mermaid-cli
+
+      - name: Write Puppeteer config (no-sandbox for CI)
+        run: |
+          echo '{"args":["--no-sandbox","--disable-setuid-sandbox"]}' > /tmp/puppeteer-config.json
+
+      - name: Extract and validate Mermaid diagrams
+        run: |
+          node - <<'EOF'
+          const fs   = require('fs');
+          const path = require('path');
+          const { execSync } = require('child_process');
+          const os   = require('os');
+
+          function findMarkdownFiles(dir) {
+            const results = [];
+            for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+              const full = path.join(dir, entry.name);
+              if (entry.isDirectory() && entry.name !== 'node_modules' && !entry.name.startsWith('.')) {
+                results.push(...findMarkdownFiles(full));
+              } else if (entry.isFile() && entry.name.endsWith('.md')) {
+                results.push(full);
+              }
+            }
+            return results;
+          }
+
+          const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'mermaid-'));
+          let errors = 0;
+          let total  = 0;
+
+          for (const mdFile of findMarkdownFiles('.')) {
+            const content = fs.readFileSync(mdFile, 'utf8');
+            const blocks  = [...content.matchAll(/^```mermaid\n([\s\S]*?)^```/gm)];
+            if (!blocks.length) continue;
+            console.log(`\nChecking ${mdFile} (${blocks.length} diagram(s))`);
+
+            blocks.forEach((match, i) => {
+              total++;
+              const mmdFile = path.join(tmpDir, `diagram-${total}.mmd`);
+              const svgFile = path.join(tmpDir, `diagram-${total}.svg`);
+              fs.writeFileSync(mmdFile, match[1]);
+              try {
+                execSync(
+                  `mmdc -i "${mmdFile}" -o "${svgFile}" --puppeteerConfigFile /tmp/puppeteer-config.json`,
+                  { stdio: 'pipe' }
+                );
+                console.log(`  [OK]  diagram ${i + 1}`);
+              } catch (err) {
+                const msg = (err.stderr || err.stdout || '').toString().split('\n')[0];
+                console.error(`  [FAIL] diagram ${i + 1}: ${msg}`);
+                console.log(`::warning file=${mdFile}::Mermaid diagram ${i + 1} failed: ${msg}`);
+                errors++;
+              }
+            });
+          }
+
+          console.log(`\nTotal diagrams checked: ${total}. Failures: ${errors}`);
+          if (errors > 0) {
+            console.log(`::warning::${errors} Mermaid diagram(s) failed to parse.`);
+            process.exit(1);
+          }
+          EOF