hive-forge: rewrite bash CLI helper as a rust binary (closes #280)

hive-forge/src/verbs/diff.rs

@@ -0,0 +1,21 @@
+//! `diff <pr> [repo]` — print the unified diff for a PR.
+
+use anyhow::Result;
+use clap::Args as ClapArgs;
+
+use crate::client::Client;
+
+#[derive(ClapArgs)]
+pub struct Args {
+    /// PR number.
+    number: u64,
+    /// Repo override.
+    repo: Option<String>,
+}
+
+pub fn run(client: &Client, args: Args) -> Result<()> {
+    let repo = client.repo(args.repo.as_deref());
+    let diff = client.get_text(&format!("/repos/{repo}/pulls/{}.diff", args.number), "text/plain")?;
+    print!("{diff}");
+    Ok(())
+}