feat(virtualcam): add Google OAuth, enable Shkeeper payments, update Caddy rules

- Update virtualcam website and API to latest repository revisions.
- Add Google OAuth client ID and secrets decryption for Google auth.
- Enable Shkeeper BTC/USD payment processing (`BYPASS_PAYMENTS=false`) and add service dependencies.
- Update Caddy `admin_gate` IP access rules and remove redundant `admin_gate` import from app proxy.
- Configure weekly automatic Nix garbage collection (`--delete-older-than 14d`) and nix store optimization.

system/nix/default.nix

@@ -19,6 +19,16 @@
   in {
     package = pkgs.lix;
 
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 14d";
+    };
+
+    optimise = {
+      automatic = true;
+    };
+
     # pin the registry to avoid downloading and evaling a new nixpkgs version every time
     registry = lib.mapAttrs (_: v: {flake = v;}) flakeInputs;