refactor(email): externalize styles to email.css, inject via expandLinkTag

- Move @import "@maizzle/tailwindcss" + @theme tokens to packages/email/email.css
- Layout uses <link rel="stylesheet" href="{{ cssPath }}" inline> — Maizzle's
  expandLinkTag reads the absolute path and expands it to a <style> tag, which
  the second compileCss pass then processes with @tailwindcss/postcss + LightningCSS
- render.ts passes cssPath as a local so the expression resolves inside the layout
- Layout head is now clean HTML with no inline style logic

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/email/src/render.ts

@@ -1,10 +1,11 @@
 import { readFile } from "node:fs/promises";
 import path from "node:path";
 
-// Templates live at packages/email/templates/
 // At runtime (dist/render.js), __dirname is packages/email/dist/
 const PKG_ROOT = path.join(__dirname, "..");
 const TEMPLATES_ROOT = path.join(PKG_ROOT, "templates");
+const CSS_PATH = path.join(PKG_ROOT, "email.css");
+
 const BASE_URL = process.env.PUBLIC_URL ?? "https://sexy.pivoine.art";
 
 export interface RenderOptions {
@@ -26,14 +27,15 @@ export async function renderTemplate(
       root: TEMPLATES_ROOT,
       folders: ["layouts"],
     },
-    // Override PostCSS `from` so @tailwindcss/postcss resolves @import "@maizzle/tailwindcss"
-    // from this package's node_modules (defu gives our value priority over the cwd default).
+    // Override PostCSS `from` so @import "@maizzle/tailwindcss" resolves
+    // from this package's node_modules (defu gives our value priority).
     postcss: {
       options: {
-        from: path.join(PKG_ROOT, "email.css"),
+        from: CSS_PATH,
       },
     },
     locals: {
+      cssPath: CSS_PATH,   // layout uses {{ cssPath }} in <link href="{{ cssPath }}" inline>
       baseUrl: BASE_URL,
       ...locals,
     },