Add portfolio template to combined marketing+portfolio template

- Added portfolio pages: portfolio-index, portfolio-about, portfolio-contact
- Added work/[slug].astro for project detail pages
- Added PortfolioBase.astro layout with Playfair Display font
- Added ProjectCard.astro component
- Added projects collection with taxonomies (category, tag)
- Updated theme.css with --font-serif variable
- Added portfolio seed data with 4 projects
- Updated menus to include Work link

.astro/fonts.d.ts

@@ -0,0 +1,4 @@
+declare module 'astro:assets' {
+	/** @internal */
+	export type CssVariable = (["--font-emdash"])[number];
+}