nixos/git: Buffer uploads on the state volume

Gitea writes uploaded release assets to a temp file before storing
them. That landed in `/tmp`, which is on the 2G tmpfs root, so
uploading the installer ISO failed with:

  ParseMultipartForm [E] ... write /tmp/multipart-...: no space
  left on device

Point the service's `TMPDIR` at the state volume, which has room.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nixos/boxes/colony/vms/git/gitea.nix

@@ -43,9 +43,19 @@ in
 
               (umask 027; gitea_extra_setup)
             '';
+
+            # Uploaded release assets are buffered through a temp file before being stored.
+            # The default /tmp is on the small tmpfs root, so keep them on the state volume.
+            environment.TMPDIR = "${config.services.gitea.stateDir}/tmp";
           }
         ];
       };
+
+      tmpfiles.settings."10-gitea-tmp"."${config.services.gitea.stateDir}/tmp".d = {
+        user = config.services.gitea.user;
+        group = config.services.gitea.group;
+        mode = "0700";
+      };
     };
 
     services = {