feat(neogaia): declare a 2 GiB EFI system partition (task 0016)

Each generation stores a kernel and an initrd on the EFI system partition,
and this host runs a large third-party kernel, so 512 MiB holds only about
seven. An exhausted partition fails at bootloader installation, after the
build has already succeeded.

The partition cannot grow in place: it sits first on the disk with the
encrypted container immediately behind it, and an encrypted volume's start
offset cannot move without rewriting its whole payload. Only an install
applies this layout, so the change takes effect at the next reimage and
does nothing to the running machine until then.

Record that a flake only sees git-tracked files, which cost an evaluation
earlier, and correct the git identity gotcha that a hand-written gitconfig
had made false.

hosts/neogaia/disk.nix

@@ -10,7 +10,9 @@
       type = "gpt";
       partitions = {
         ESP = {
-          size = "512M";
+          # Each generation stores a kernel and initrd here and the CachyOS
+          # kernel is large; an exhausted partition fails bootloader installs.
+          size = "2G";
           type = "EF00";
           content = {
             type = "filesystem";