fix(catppuccin): drop the ignored user-level cache entry

Catppuccin's home-manager module writes extra-substituters/extra-trusted-public-keys
for catppuccin.cachix.org into the user-level ~/.config/nix/nix.conf. Since the
normal user is no longer a trusted-user (modules/base/nix.nix), Nix ignores those
client-specified settings and warns on every command. The ports build locally, so
turn the user-level cache off instead.

home/base/core/theme.nix

@@ -10,7 +10,10 @@
     enable = true;
     # Enroll every supported port (catppuccin/nix >= main behaviour).
     autoEnable = true;
-    cache.enable = true;
+    # Catppuccin's ports build locally, and the user-level cache entry this
+    # adds to ~/.config/nix/nix.conf would be ignored (with a warning) now that
+    # the normal user is not a trusted-user. See modules/base/nix.nix.
+    cache.enable = false;
     # one of "latte", "frappe", "macchiato", "mocha"
     flavor = "mocha";
     # one of "blue", "flamingo", "green", "lavender", "maroon", "mauve", "peach", "pink", "red", "rosewater", "sapphire", "sky", "teal", "yellow"