Reduce miniflux feed refresh batch size to 15 (#238)

The default BATCH_SIZE of 100 causes network issues due to too many
domains being fetched concurrently. Lower it to 15 to reduce load.

https://claude.ai/code/session_01SDH1DWoiQ8dEPA6kFskffE

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Co-authored-by: Claude <noreply@anthropic.com>

Author: akrantz01

components/miniflux.nix

@@ -70,6 +70,11 @@ in {
       config = {
         BASE_URL = "https://${cfg.domain}";
         HTTPS = 1;
+        BATCH_SIZE = 15;
+        POLLING_FREQUENCY = 60;
+        POLLING_SCHEDULER = "entry_frequency";
+        SCHEDULER_ENTRY_FREQUENCY_MIN_INTERVAL = 60;
+        SCHEDULER_ENTRY_FREQUENCY_MAX_INTERVAL = 1440;
 
         DISABLE_LOCAL_AUTH = 1;