Add Project IDX configuration files

This commit adds the necessary configuration files to support opening and building the project in Project IDX.

The new files are:
- `idx.json`: Specifies the tools and build tasks for the project.
- `.idx/dev.nix`: Defines the development environment, including the required JDK, Android SDK, and system dependencies.

.idx/dev.nix

@@ -0,0 +1,31 @@
+{ pkgs, ... }: {
+  # Entorno de desarrollo para uHabits
+  channel = "stable-23.11"; # O la versión que prefieras
+
+  packages = [
+    pkgs.unzip
+    pkgs.wget
+  ];
+
+  # Configuración del JDK y Android SDK
+  languages.java.enable = true;
+  languages.java.jdk.package = pkgs.openjdk17;
+
+  # Habilitar el SDK de Android
+  android.sdk.enable = true;
+  android.sdk.platforms = ["34"]; # API level 34
+  android.sdk.buildTools = ["34.0.0"];
+  android.sdk.platformTools.enable = true;
+  android.sdk.cmdLineTools.enable = true;
+  android.sdk.emulator.enable = true;
+
+  # Variables de entorno
+  env.JAVA_HOME = "${pkgs.openjdk17}/";
+  env.ANDROID_HOME = "$HOME/.android/sdk";
+  env.PATH = [
+    "$ANDROID_HOME/cmdline-tools/latest/bin",
+    "$ANDROID_HOME/platform-tools",
+    "$ANDROID_HOME/emulator",
+    "$JAVA_HOME/bin"
+  ];
+}

idx.json

@@ -0,0 +1,15 @@
+{
+  "version": 1,
+  "tools": {
+    "android": {
+      "version": "34.0.0"
+    },
+    "java": {
+      "version": "17"
+    }
+  },
+  "build": {
+    "builder": "gradle",
+    "tasks": ["assembleDebug"]
+  }
+}