REFACTORED - Flatten portfolio category routes to /portfolio/[slug]

Merge the category and project routes under a single /portfolio/[slug]
segment via resolvePortfolioSlug (category wins over project on a slug
clash). Removes the /portfolio/category/... prefix from links, redirect,
and sitemap. Adds resolver integration tests.

app/[locale]/(site)/portfolio/[slug]/page.tsx

@@ -4,16 +4,20 @@ import { notFound } from "next/navigation";
 
 import { Container } from "@/components/layout/container";
 import { PageHero } from "@/components/layout/page-hero";
+import { PortfolioCategoryFilter } from "@/components/site/portfolio-category-filter";
 import { PortfolioProjectDetail } from "@/components/site/portfolio-project-detail";
+import { PortfolioProjectGrid } from "@/components/site/portfolio-project-grid";
 import { getSiteSettings } from "@/lib/app-config";
 import { buildLocalizedMetadata } from "@/lib/metadata";
 import { resolveLocale } from "@/lib/locale";
 import {
+  getActivePortfolioCategories,
   getLocalizedValue,
-  getPublishedPortfolioProjectBySlug,
+  getPublishedPortfolioProjects,
+  resolvePortfolioSlug,
 } from "@/lib/portfolio";
 
-type PortfolioItemPageProps = {
+type PortfolioSlugPageProps = {
   params: Promise<{
     locale: string;
     slug: string;
@@ -22,41 +26,88 @@ type PortfolioItemPageProps = {
 
 export const dynamic = "force-dynamic";
 
-export async function generateMetadata({ params }: PortfolioItemPageProps): Promise<Metadata> {
+export async function generateMetadata({ params }: PortfolioSlugPageProps): Promise<Metadata> {
   const { slug } = await params;
   const siteSettings = await getSiteSettings();
   const localeKey = resolveLocale(await getLocale().catch(() => siteSettings.defaultLocale), siteSettings.defaultLocale);
-  const item = await getPublishedPortfolioProjectBySlug(slug);
+  const resolved = await resolvePortfolioSlug(slug);
 
-  if (!item) {
+  if (!resolved) {
+    const t = await getTranslations({ locale: localeKey, namespace: "portfolioPage" });
     return await buildLocalizedMetadata({
       locale: localeKey,
       pathname: `/portfolio/${slug}`,
-      title: "Portfolio",
-      description: "Portfolio item",
+      title: t("title"),
+      description: t("intro"),
+    });
+  }
+
+  if (resolved.kind === "category") {
+    const t = await getTranslations({ locale: localeKey, namespace: "portfolioPage" });
+    return await buildLocalizedMetadata({
+      locale: localeKey,
+      pathname: `/portfolio/${slug}`,
+      title: getLocalizedValue(resolved.category.name, localeKey),
+      description: getLocalizedValue(resolved.category.description, localeKey) || t("intro"),
     });
   }
 
   return await buildLocalizedMetadata({
     locale: localeKey,
     pathname: `/portfolio/${slug}`,
-    title: getLocalizedValue(item.title, localeKey),
-    description: getLocalizedValue(item.summary, localeKey),
+    title: getLocalizedValue(resolved.project.title, localeKey),
+    description: getLocalizedValue(resolved.project.summary, localeKey),
   });
 }
 
-export default async function PortfolioItemPage({
-  params,
-}: PortfolioItemPageProps) {
+export default async function PortfolioSlugPage({ params }: PortfolioSlugPageProps) {
   const { slug } = await params;
   const siteSettings = await getSiteSettings();
   const localeKey = resolveLocale(await getLocale().catch(() => siteSettings.defaultLocale), siteSettings.defaultLocale);
-  const item = await getPublishedPortfolioProjectBySlug(slug);
+  const resolved = await resolvePortfolioSlug(slug);
 
-  if (!item) {
+  if (!resolved) {
     notFound();
   }
 
+  if (resolved.kind === "category") {
+    const { category } = resolved;
+    const [categories, projects] = await Promise.all([
+      getActivePortfolioCategories(),
+      getPublishedPortfolioProjects({ categorySlug: slug }),
+    ]);
+    const t = await getTranslations({ locale: localeKey, namespace: "portfolioPage" });
+
+    return (
+      <>
+        <PageHero
+          locale={localeKey}
+          badge={t("heroBadge")}
+          title={getLocalizedValue(category.name, localeKey)}
+          description={getLocalizedValue(category.description, localeKey) || t("intro")}
+        />
+
+        <Container className="flex flex-col gap-section pb-12 lg:pb-16">
+          <PortfolioCategoryFilter
+            locale={localeKey}
+            defaultLocale={siteSettings.defaultLocale}
+            categories={categories}
+            allLabel={t("all")}
+            activeCategorySlug={category.slug}
+          />
+          <PortfolioProjectGrid
+            locale={localeKey}
+            defaultLocale={siteSettings.defaultLocale}
+            projects={projects}
+            emptyLabel={t("empty")}
+            openLabel={t("open")}
+          />
+        </Container>
+      </>
+    );
+  }
+
+  const { project: item } = resolved;
   const t = await getTranslations({ locale: localeKey, namespace: "portfolioDetail" });
   const title = getLocalizedValue(item.title, localeKey);
   const category = getLocalizedValue(item.category.name, localeKey);