refactor: remove redundant .gitconfig tmpfiles rule, use GIT_INIT_DEFAULT_BRANCH env var

The .gitconfig at /home/hermes/.gitconfig was never read because the
hermes-agent service sets HOME=/var/lib/hermes. Git identity was already
fully covered by GIT_AUTHOR_* and GIT_COMMITTER_* env vars via .env.

Replace the dead .gitconfig's init.defaultBranch with the env var
GIT_INIT_DEFAULT_BRANCH (supported since Git 2.28).

hosts/m3-atlas/services/redis.nix

@@ -0,0 +1,16 @@
+{config, ...}: {
+  services.redis.servers.honcho = {
+    enable = true;
+    port = 6380; # Separate from default Redis (6379) to avoid conflicts
+    bind = "127.0.0.1";
+    save = [
+      [900 1]
+      [300 10]
+      [60 10000]
+    ];
+  };
+
+  networking.firewall.extraCommands = ''
+    iptables -A INPUT -p tcp -s 127.0.0.1 --dport 6380 -j ACCEPT
+  '';
+}