refactor(viridian): migrate service data to dedicated BTRFS subvolumes

Migrate from path-based persistence (/persist/var/lib/*) to dedicated
BTRFS subvolumes for better data isolation and snapshot capabilities.

- Move valuable user-facing services to /srv/* with srv-* subvolumes:
  - forgejo: git repositories and database
  - opengist: paste data
  - minecraft: game world data
  - lighttpd: static web content
  - containers: OCI container volumes

- Update home directory to use hm-sajenim subvolume on viridian disk
- Remove jupyterhub service (no longer in use)
- Update borgbackup paths to match new service locations
- Follow upstream service defaults where possible for maintainability

Services kept on /persist (disposable state):
- traefik, crowdsec, murmur

nixos/viridian/multimedia/default.nix

@@ -1,4 +1,6 @@
-{...}: {
+{config, ...}: let
+  hostname = config.networking.hostName;
+in {
   imports = [
     ./jellyfin
     ./lidarr
@@ -7,4 +9,17 @@
     ./radarr
     ./sonarr
   ];
+
+  fileSystems = {
+    "/srv/multimedia" = {
+      device = "/dev/disk/by-label/multimedia";
+      fsType = "ext4";
+    };
+
+    "/srv/multimedia/containers" = {
+      device = "/dev/disk/by-label/${hostname}";
+      fsType = "btrfs";
+      options = ["subvol=srv-containers" "compress=zstd"];
+    };
+  };
 }