Add clap dependency and update app for CLI integration

Update Cargo files to add clap and related dependencies, restructure App
to handle configuration from CLI, and update nix module to support
config source tracking. Add new cli module and adjust main to initialize
modules at startup.

src/cli.rs

@@ -0,0 +1,64 @@
+use crate::nix::{ConfigOption, ConfigSource, collect_nix_options};
+use clap::Parser;
+use rnix::{Parse, Root};
+use std::{fs, path::PathBuf};
+
+#[derive(Parser, Debug)]
+#[command(
+    version,
+    about = "Potrzebne pliki znajdziesz w ~/garandos/hosts/<Twój-Host>/",
+    long_about = "Potrzebne pliki znajdziesz w ~/garandos/hosts/<Twój-Host>/"
+)]
+pub struct Cli {
+    #[arg(
+        long,
+        help = "Ścieżka do pliku system-modules.nix",
+        value_name = "SYSTEM_MODULES"
+    )]
+    pub sf: PathBuf,
+    #[arg(
+        long,
+        help = "Ścieżka do pliku home-modules.nix",
+        value_name = "HOME_MODULES"
+    )]
+    pub hf: PathBuf,
+}
+
+pub struct NixModules {
+    pub system_modules: Vec<ConfigOption>,
+    pub home_modules: Vec<ConfigOption>,
+}
+
+pub fn get_modules() -> NixModules {
+    let args: Cli = Cli::parse();
+
+    let system_file: String = fs::read_to_string(&args.sf).expect("Failed to read system file");
+    let home_file: String = fs::read_to_string(&args.hf).expect("Failed to read home file");
+
+    let system_ast: Parse<Root> = get_ast(&system_file);
+    let home_ast: Parse<Root> = get_ast(&home_file);
+
+    let system_modules: Vec<ConfigOption> =
+        collect_nix_options(&system_ast.syntax(), "", ConfigSource::System);
+    let home_modules: Vec<ConfigOption> =
+        collect_nix_options(&home_ast.syntax(), "", ConfigSource::Home);
+
+    NixModules {
+        system_modules,
+        home_modules,
+    }
+}
+
+fn get_ast(file: &str) -> Parse<Root> {
+    let ast: Parse<Root> = Root::parse(&file);
+
+    if !ast.errors().is_empty() {
+        eprintln!("Błędy parsowania:");
+        for error in ast.errors() {
+            eprintln!("  - {}", error);
+        }
+        panic!("Błąd z parsowaniem pliku .nix")
+    }
+
+    ast
+}