feat: Vikunja to-do app (#128)

Vikunja is fast self-hostable to-do app.

Reviewed-on: https://git.selfprivacy.org/SelfPrivacy/selfprivacy-nixos-config/pulls/128
Reviewed-by: Inex Code <inex.code@selfprivacy.org>
Co-authored-by: nhnn <nhnn@nhnn.dev>
Co-committed-by: nhnn <nhnn@nhnn.dev>

sp-modules/vikunja/flake.nix

@@ -0,0 +1,41 @@
+{
+  description = "PoC SP module for Vikunja service";
+
+  inputs = {
+    nixpkgs-24-11.url = "github:NixOS/nixpkgs/nixos-24.11";
+  };
+
+  outputs = {nixpkgs-24-11, ...}: {
+    nixosModules.default = import ./module.nix nixpkgs-24-11.legacyPackages.x86_64-linux;
+    configPathsNeeded =
+      builtins.fromJSON (builtins.readFile ./config-paths-needed.json);
+    meta = {lib, ...}: {
+      spModuleSchemaVersion = 1;
+      id = "vikunja";
+      name = "Vikunja";
+      description = "Vikunja, the fluffy, open-source, self-hostable to-do app.";
+      svgIcon = builtins.readFile ./icon.svg;
+      isMovable = true;
+      isRequired = false;
+      backupDescription = "Tasks and attachments.";
+      systemdServices = [
+        "vikunja.service"
+      ];
+      folders = [
+        "/var/lib/vikunja"
+      ];
+      postgreDatabases = [
+        "vikunja"
+      ];
+      license = [
+        lib.licenses.agpl3Plus
+      ];
+      homepage = "https://vikunja.io";
+      sourcePage = "https://github.com/go-vikunja/vikunja";
+      supportLevel = "normal";
+      sso = {
+        userGroup = "sp.vikunja.users";
+      };
+    };
+  };
+}