feat: Improve admin command reference generation

- Change xtasks to use `clap` for argument parsing
- Generate admin command reference manually instead of with `clap_markdown`
- Split admin command reference into multiple files

xtask/src/main.rs

@@ -0,0 +1,26 @@
+mod tasks;
+
+use clap::Parser;
+
+use crate::tasks::Task;
+
+#[derive(clap::Parser)]
+struct BaseArgs {
+	#[command(subcommand)]
+	task: Task,
+	#[command(flatten)]
+	args: Args,
+}
+
+#[derive(clap::Args)]
+struct Args {
+	/// Simulate without actually touching the filesystem
+	#[arg(long)]
+	dry_run: bool,
+}
+
+fn main() -> impl std::process::Termination {
+	let BaseArgs { task, args } = BaseArgs::parse();
+
+	task.invoke(args)
+}