fix(og): match plain URL slugs; fix Funkwhale GC wipe

og-fix transform was matching date-based URL segments
(/type/yyyy/MM/dd/slug/) that this site never uses — posts live at
/type/slug/. Every post therefore fell through to the default OG image.

Fixed by updating the regex to /type/slug/index.html and deriving the OG
slug as the bare last URL segment, which matches the filename og.js
already generates. The ogSlug filter is simplified accordingly.

Funkwhale GC bug: gcFunkwhaleImages() deleted the entire image cache
whenever _activeFilenames was empty — which happens if the API returns
valid stats but no listenings with cover URLs. Guard added: GC is
skipped when no images were referenced this build.

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

lib/cache-funkwhale-image.js

@@ -76,6 +76,10 @@ export async function cacheFunkwhaleImage(url) {
  */
 export function gcFunkwhaleImages() {
   if (!existsSync(CACHE_DIR)) return;
+  // If no images were referenced this build, skip GC — likely the API returned no
+  // cover URLs (empty listenings, null covers, or stats-only response). Deleting
+  // everything from an empty _activeFilenames set would wipe a valid cache.
+  if (_activeFilenames.size === 0) return;
   let deleted = 0;
   for (const file of readdirSync(CACHE_DIR)) {
     if (!_activeFilenames.has(file)) {

lib/og.js

@@ -126,7 +126,8 @@ function formatDate(dateStr) {
 }
 
 /**
- * Use the full filename (with date prefix) as the OG image slug.
+ * Use the filename (without extension) as the OG image slug.
+ * Matches the last URL path segment, which Eleventy derives from the filename.
  */
 function toOgSlug(filename) {
   return filename;