alexandria: replace FreshRSS with Miniflux

- Add miniflux service listening on Unix socket at /run/miniflux/miniflux.sock
- Remove FreshRSS configuration and data directory
- Update nginx to reverse proxy to miniflux socket
- Update secrets to use miniflux-admincreds.age

data/services.nix

@@ -34,7 +34,7 @@
       host = "alexandria";
     }
     {
-      name = "freshrss";
+      name = "miniflux";
       domain = "rss.baduhai.dev";
       host = "alexandria";
     }