refactor(ops): Split //ops/nixos into different locations

Splits //ops/nixos into:

* //ops/nixos.nix - utility functions for building systems
* //ops/machines - shared machine definitions (read by readTree)
* //ops/modules - shared NixOS modules (skipped by readTree)

This simplifies working with the configuration fixpoint in whitby, and
is overall a bit more in line with how NixOS systems in user folders
currently work.

Change-Id: I1322ec5cc76c0207c099c05d44828a3df0b3ffc1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2931
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: glittershark <grfn@gws.fyi>

ops/modules/www/code.tvl.fyi.nix

@@ -0,0 +1,35 @@
+{ depot, ... }:
+
+{
+  imports = [
+    ./base.nix
+  ];
+
+  config = {
+    services.nginx.virtualHosts.cgit = {
+      serverName = "code.tvl.fyi";
+      serverAliases = [ "code.tvl.su" ];
+      enableACME = true;
+      forceSSL = true;
+
+      extraConfig = ''
+        # Serve the rendered Tvix component SVG.
+        #
+        # TODO(tazjin): Implement a way of serving this dynamically
+        location = /about/tvix/docs/component-flow.svg {
+            alias ${depot.tvix.docs.svg}/component-flow.svg;
+        }
+
+        # Static assets must always hit the root.
+        location ~ ^/(favicon\.ico|cgit\.(css|png))$ {
+           proxy_pass http://localhost:2448;
+        }
+
+        # Everything else hits the depot directly.
+        location / {
+            proxy_pass http://localhost:2448/cgit.cgi/depot/;
+        }
+      '';
+    };
+  };
+}