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/email.css

@@ -0,0 +1,18 @@
+@import "@maizzle/tailwindcss";
+
+@theme {
+  /* ── Design tokens — exact mirror of frontend app.css :root ── */
+  --color-background:         oklch(0.98 0.01 320);
+  --color-foreground:         oklch(0.08 0.02 280);
+  --color-card:               oklch(0.99 0.005 320);
+  --color-card-foreground:    oklch(0.08 0.02 280);
+  --color-muted:              oklch(0.95 0.01 280);
+  --color-muted-foreground:   oklch(0.4 0.02 280);
+  --color-border:             oklch(0.85 0.02 280);
+  --color-primary:            oklch(56.971% 0.27455 319.257);
+  --color-primary-foreground: oklch(0.98 0.01 320);
+
+  /* ── Font ── */
+  --font-sans: 'Noto Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto,
+               Helvetica, Arial, sans-serif;
+}