feat(dev): add live-reload dev server with Juice CSS inlining

- tools/server/: Node.js dev server (Express + WebSocket + fs.watch)
  Watches themes/ for .tmpl changes, rebuilds via Go preview command,
  applies Juice CSS inlining for email client compatibility, pushes
  live reload to browser via WebSocket.
- tools/cli/dev.go: 'go run . dev' subcommand — starts Node.js server
  with automatic npm install, initial preview generation, and
  Ctrl+C graceful shutdown.
- tools/tools.go: register dev command in CLI app.
- .gitignore: add node_modules exclusion.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tools/server/inliner.mjs

@@ -0,0 +1,51 @@
+import juice from 'juice';
+
+/** Juice CSS inlining options optimized for HTML email. */
+const JUICE_OPTIONS = {
+  removeStyleTags: false,    // keep <style> for modern clients that support it
+  preserveMediaQueries: true,
+  preserveFontFaces: true,
+  applyWidthAttributes: true,
+  applyHeightAttributes: true,
+  applyAttributesTableElements: true,
+  xmlMode: false,
+};
+
+/**
+ * Inline CSS from <style> blocks and <link> tags into inline style attributes.
+ * Produces HTML that renders consistently across Gmail, Outlook, Apple Mail.
+ */
+export function inlineCSS(html) {
+  return juice(html, JUICE_OPTIONS);
+}
+
+/**
+ * Apply juice inlining to a rendered.js-style HTML snippet and return the
+ * result. Handles escaped HTML (JSON-stringified) by first unescaping,
+ * inlining, then re-escaping for storage in rendered.js.
+ */
+export function inlineRenderedHTML(rawhtml) {
+  try {
+    // If this is already a standalone HTML document fragment
+    if (rawhtml.includes('<style') || rawhtml.includes('</style>')) {
+      return inlineCSS(rawhtml);
+    }
+    // Otherwise pass through unchanged (inline-only content)
+    return rawhtml;
+  } catch (err) {
+    console.error('Juice inline error:', err.message);
+    return rawhtml;
+  }
+}
+
+if (process.argv[1] && import.meta.url.endsWith(process.argv[1])) {
+  // CLI mode: juice <input> [output]
+  const { readFileSync, writeFileSync } = await import('fs');
+  const input = process.argv[2];
+  const output = process.argv[3];
+  if (!input) { console.error('Usage: node inliner.mjs <input.html> [output.html]'); process.exit(1); }
+  const html = readFileSync(input, 'utf8');
+  const result = inlineCSS(html);
+  if (output) { writeFileSync(output, result, 'utf8'); console.log(`Inlined → ${output}`); }
+  else { console.log(result); }
+}