perf: reduce history page size from 100 to 20

- SABnzbd, Sonarr, and Radarr history now fetch 20 items instead of 100
- Only recent completions are needed for the dashboard
- Reduces response payload and serialization time

server/routes/dashboard.js

@@ -148,7 +148,7 @@ router.get('/user-downloads', async (req, res) => {
     
     const sabHistoryPromises = sabInstances.map(inst => 
       axios.get(`${inst.url}/api`, {
-        params: { mode: 'history', apikey: inst.apiKey, output: 'json', limit: 100 }
+        params: { mode: 'history', apikey: inst.apiKey, output: 'json', limit: 20 }
       }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
         console.error(`[Dashboard] SABnzbd ${inst.id} history error:`, err.message);
         return { instance: inst.id, data: { history: { slots: [] } } };
@@ -180,7 +180,7 @@ router.get('/user-downloads', async (req, res) => {
     const sonarrHistoryPromises = sonarrInstances.map(inst => 
       axios.get(`${inst.url}/api/v3/history`, {
         headers: { 'X-Api-Key': inst.apiKey },
-        params: { pageSize: 100, includeSeries: true, includeEpisode: true }
+        params: { pageSize: 20, includeSeries: true, includeEpisode: true }
       }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
         console.error(`[Dashboard] Sonarr ${inst.id} history error:`, err.message);
         return { instance: inst.id, data: { records: [] } };
@@ -212,7 +212,7 @@ router.get('/user-downloads', async (req, res) => {
     const radarrHistoryPromises = radarrInstances.map(inst => 
       axios.get(`${inst.url}/api/v3/history`, {
         headers: { 'X-Api-Key': inst.apiKey },
-        params: { pageSize: 100, includeMovie: true }
+        params: { pageSize: 20, includeMovie: true }
       }).then(res => ({ instance: inst.id, data: res.data })).catch(err => {
         console.error(`[Dashboard] Radarr ${inst.id} history error:`, err.message);
         return { instance: inst.id, data: { records: [] } };