fix(tags): normalize nested category paths for ActivityPub hashtags

Nested categories like `on/tech` or `art/music` were being sent as-is
to ActivityPub consumers. Three fixes:

- status.js (Mastodon Client API): raw category used as tag name/URL
  instead of the normalized last segment
- jf2-to-as2.js buildPlainTags/buildFedifyTags: href used
  encodeURIComponent() on the full path, encoding the `/` separator
  and producing broken category URLs (e.g. `categories/on%2Ftech`
  instead of `categories/on/tech`)

Tag names are now consistently normalized to the last path segment
(`on/tech` → `#tech`). Category hrefs encode each segment individually
but preserve the `/` separator.

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

lib/jf2-to-as2.js

@@ -621,10 +621,12 @@ function buildPlainTags(properties, publicationUrl, existing) {
   const tags = [...(existing || [])];
   if (properties.category) {
     for (const cat of asArray(properties.category)) {
+      const normalized = cat.split("/").at(-1).replace(/\s+/g, "");
+      const segments = cat.split("/").map((s) => encodeURIComponent(s.replace(/\s+/g, "")));
       tags.push({
         type: "Hashtag",
-        name: `#${cat.split("/").at(-1).replace(/\s+/g, "")}`,
-        href: `${publicationUrl}categories/${encodeURIComponent(cat)}`,
+        name: `#${normalized}`,
+        href: `${publicationUrl}categories/${segments.join("/")}`,
       });
     }
   }
@@ -643,12 +645,12 @@ function buildFedifyTags(properties, publicationUrl, postType) {
   }
   if (properties.category) {
     for (const cat of asArray(properties.category)) {
+      const normalized = cat.split("/").at(-1).replace(/\s+/g, "");
+      const segments = cat.split("/").map((s) => encodeURIComponent(s.replace(/\s+/g, "")));
       tags.push(
         new Hashtag({
-          name: `#${cat.split("/").at(-1).replace(/\s+/g, "")}`,
-          href: new URL(
-            `${publicationUrl}categories/${encodeURIComponent(cat)}`,
-          ),
+          name: `#${normalized}`,
+          href: new URL(`${publicationUrl}categories/${segments.join("/")}`),
         }),
       );
     }

lib/mastodon/entities/status.js

@@ -173,11 +173,14 @@ export function serializeStatus(item, { baseUrl, favouritedIds, rebloggedIds, bo
   // Link preview -> card
   const card = serializeCard(item.linkPreviews?.[0]);
 
-  // Tags from category[]
-  const tags = (item.category || []).map((tag) => ({
-    name: tag,
-    url: `${baseUrl}/tags/${encodeURIComponent(tag)}`,
-  }));
+  // Tags from category[] — normalize nested paths (e.g. "on/tech" → "tech")
+  const tags = (item.category || []).map((tag) => {
+    const normalized = tag.split("/").at(-1).replace(/\s+/g, "");
+    return {
+      name: normalized,
+      url: `${baseUrl}/tags/${encodeURIComponent(normalized)}`,
+    };
+  });
 
   // Mentions — use actorUrl for deterministic ID, parse acct from handle
   const mentions = (item.mentions || []).map((m) => {