hive-forge: add 'reopen' verb (pr reopen / issue reopen)

hive-forge had close but no reopen, so reopening required the non-obvious
workaround 'issue edit <n> --state open'. Add a reopen verb mirroring close
(PATCH state=open), wired into both 'pr reopen' (kind-checked PR) and
'issue reopen' (kind-checked issue). Updates docs/forge.md + the subcommand
enumerations.

hive-forge/src/verbs/reopen.rs

@@ -0,0 +1,30 @@
+//! `reopen <number>` — reopen a closed issue or PR.
+//!
+//! Mirror of `close`: sends a PATCH setting the issue/PR `state` back to
+//! `open`. PRs share the issue number space, so the same `/issues/<n>`
+//! endpoint reopens either.
+
+use anyhow::Result;
+use clap::Args as ClapArgs;
+use serde_json::json;
+
+use crate::client::Client;
+use crate::verbs::print_json;
+
+#[derive(ClapArgs)]
+pub struct Args {
+    /// Issue or PR number.
+    pub(crate) number: u64,
+}
+
+pub fn run(client: &Client, args: Args) -> Result<()> {
+    let repo = client.repo();
+    let resp = client.patch_json(
+        &format!("/repos/{repo}/issues/{}", args.number),
+        &json!({ "state": "open" }),
+    )?;
+    print_json(&json!({
+        "number": resp.get("number"),
+        "state": resp.get("state"),
+    }))
+}