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/common/users/sajenim/default.nix

@@ -4,7 +4,9 @@
   pkgs,
   config,
   ...
-}: {
+}: let
+  hostname = config.networking.hostName;
+in {
   imports = [
     inputs.home-manager.nixosModules.home-manager
   ];
@@ -29,8 +31,8 @@
   };
 
   fileSystems."/home/sajenim" = {
-    device = "/dev/disk/by-label/data";
+    device = "/dev/disk/by-label/${hostname}";
     fsType = "btrfs";
-    options = ["subvol=sajenim" "compress=zstd"];
+    options = ["subvol=hm-sajenim" "compress=zstd"];
   };
 }