fix(seo): URL-encode tag in canonical link

Tag pages emitted <link rel="canonical" href="...tag/Foo Bar/">
with literal spaces. Wrap with encodeURIComponent so the canonical
matches the encoded URL in the sitemap.

src/pages/tag/[tag]/index.astro

@@ -28,7 +28,7 @@ const page = {
   },
 };
 
-const canonical = `${site.url}/tag/${tag}/`;
+const canonical = `${site.url}/tag/${encodeURIComponent(tag)}/`;
 ---
 <Layout
   title={`Tagged: ${tag} — ${site.name}`}

src/pages/tag/[tag]/page/[page]/index.astro

@@ -43,7 +43,7 @@ const page = {
   },
 };
 
-const canonical = `${site.url}/tag/${tag}/page/${currentPage}/`;
+const canonical = `${site.url}/tag/${encodeURIComponent(tag)}/page/${currentPage}/`;
 ---
 <Layout
   title={`Tagged: ${tag} — Page ${currentPage} — ${site.name}`}