perf: cache slow-changing data (series, movies, tags) with 60s TTL

- Add MemoryCache utility with get/set/invalidate/clear
- Cache Sonarr series, Sonarr tags, Radarr movies, Radarr tags
- 60-second TTL - first request fetches, subsequent requests served from cache
- Queue, history, and torrent data remain uncached (changes frequently)
- On cache hit, these 4 heavy API calls resolve instantly

server/routes/dashboard.js

@@ -8,6 +8,9 @@ const {
   getSonarrInstances, 
   getRadarrInstances 
 } = require('../utils/config');
+const cache = require('../utils/cache');
+
+const CACHE_TTL = 60 * 1000; // 60 seconds for slow-changing data (series, movies, tags)
 
 const EMBY_URL = process.env.EMBY_URL;
 const EMBY_API_KEY = process.env.EMBY_API_KEY;
@@ -94,6 +97,19 @@ function getRadarrLink(movie) {
   return `${movie._instanceUrl}/movie/${movie.titleSlug}`;
 }
 
+// Cached fetch helper - returns cached data if available, otherwise fetches and caches
+async function cachedFetch(cacheKey, fetchFn, ttl = CACHE_TTL) {
+  const cached = cache.get(cacheKey);
+  if (cached) {
+    console.log(`[Dashboard] Cache HIT: ${cacheKey}`);
+    return cached;
+  }
+  console.log(`[Dashboard] Cache MISS: ${cacheKey}`);
+  const data = await fetchFn();
+  cache.set(cacheKey, data, ttl);
+  return data;
+}
+
 // Get user downloads for authenticated user
 router.get('/user-downloads', async (req, res) => {
   try {
@@ -139,14 +155,16 @@ router.get('/user-downloads', async (req, res) => {
       })
     );
     
-    // Fetch from all Sonarr instances
-    const sonarrTagsPromises = sonarrInstances.map(inst => 
-      axios.get(`${inst.url}/api/v3/tag`, {
-        headers: { 'X-Api-Key': inst.apiKey }
-      }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
-        console.error(`[Dashboard] Sonarr ${inst.id} tags error:`, err.message);
-        return { instance: inst.id, data: [] };
-      })
+    // Fetch from all Sonarr instances (tags cached)
+    const sonarrTagsPromise = cachedFetch('sonarr-tags', () => 
+      Promise.all(sonarrInstances.map(inst => 
+        axios.get(`${inst.url}/api/v3/tag`, {
+          headers: { 'X-Api-Key': inst.apiKey }
+        }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
+          console.error(`[Dashboard] Sonarr ${inst.id} tags error:`, err.message);
+          return { instance: inst.id, data: [] };
+        })
+      ))
     );
     
     const sonarrQueuePromises = sonarrInstances.map(inst => 
@@ -169,13 +187,15 @@ router.get('/user-downloads', async (req, res) => {
       })
     );
     
-    const sonarrSeriesPromises = sonarrInstances.map(inst => 
-      axios.get(`${inst.url}/api/v3/series`, {
-        headers: { 'X-Api-Key': inst.apiKey }
-      }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
-        console.error(`[Dashboard] Sonarr ${inst.id} series error:`, err.message);
-        return { instance: inst.id, data: [] };
-      })
+    const sonarrSeriesPromise = cachedFetch('sonarr-series', () => 
+      Promise.all(sonarrInstances.map(inst => 
+        axios.get(`${inst.url}/api/v3/series`, {
+          headers: { 'X-Api-Key': inst.apiKey }
+        }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
+          console.error(`[Dashboard] Sonarr ${inst.id} series error:`, err.message);
+          return { instance: inst.id, data: [] };
+        })
+      ))
     );
     
     // Fetch from all Radarr instances
@@ -199,25 +219,29 @@ router.get('/user-downloads', async (req, res) => {
       })
     );
     
-    const radarrMoviesPromises = radarrInstances.map(inst => 
-      axios.get(`${inst.url}/api/v3/movie`, {
-        headers: { 'X-Api-Key': inst.apiKey }
-      }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
-        console.error(`[Dashboard] Radarr ${inst.id} movies error:`, err.message);
-        return { instance: inst.id, data: [] };
-      })
+    const radarrMoviesPromise = cachedFetch('radarr-movies', () => 
+      Promise.all(radarrInstances.map(inst => 
+        axios.get(`${inst.url}/api/v3/movie`, {
+          headers: { 'X-Api-Key': inst.apiKey }
+        }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
+          console.error(`[Dashboard] Radarr ${inst.id} movies error:`, err.message);
+          return { instance: inst.id, data: [] };
+        })
+      ))
     );
     
-    const radarrTagsPromises = radarrInstances.map(inst => 
-      axios.get(`${inst.url}/api/v3/tag`, {
-        headers: { 'X-Api-Key': inst.apiKey }
-      }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
-        console.error(`[Dashboard] Radarr ${inst.id} tags error:`, err.message);
-        return { instance: inst.id, data: [] };
-      })
+    const radarrTagsPromise = cachedFetch('radarr-tags', () => 
+      Promise.all(radarrInstances.map(inst => 
+        axios.get(`${inst.url}/api/v3/tag`, {
+          headers: { 'X-Api-Key': inst.apiKey }
+        }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
+          console.error(`[Dashboard] Radarr ${inst.id} tags error:`, err.message);
+          return { instance: inst.id, data: [] };
+        })
+      ))
     );
     
-    // Execute all requests
+    // Execute all requests (cached items resolve instantly on cache hit)
     const [
       sabQueues, sabHistories, sonarrTagsResults, sonarrQueues, sonarrHistories, sonarrSeriesResults,
       radarrQueues, radarrHistories, radarrMoviesResults, radarrTagsResults,
@@ -225,14 +249,14 @@ router.get('/user-downloads', async (req, res) => {
     ] = await Promise.all([
       Promise.all(sabQueuePromises),
       Promise.all(sabHistoryPromises),
-      Promise.all(sonarrTagsPromises),
+      sonarrTagsPromise,
       Promise.all(sonarrQueuePromises),
       Promise.all(sonarrHistoryPromises),
-      Promise.all(sonarrSeriesPromises),
+      sonarrSeriesPromise,
       Promise.all(radarrQueuePromises),
       Promise.all(radarrHistoryPromises),
-      Promise.all(radarrMoviesPromises),
-      Promise.all(radarrTagsPromises),
+      radarrMoviesPromise,
+      radarrTagsPromise,
       getTorrents().catch(err => {
         console.error(`[Dashboard] qBittorrent error:`, err.message);
         return [];