hive-forge: add body to pr show --json, error --json on six verbs that silently ignored it

hive-forge/src/verbs/tree_sha.rs

@@ -1,7 +1,7 @@
 //! `tree-sha <ref> [repo]` — print the tree SHA of the commit at a
 //! branch name or commit SHA.
 
-use anyhow::Result;
+use anyhow::{Result, bail};
 use clap::Args as ClapArgs;
 use forgejo_api::structs::RepoGetSingleCommitQuery;
 
@@ -14,6 +14,9 @@ pub struct Args {
 }
 
 pub fn run(client: &Client, args: Args) -> Result<()> {
+    if client.json_mode() {
+        bail!("hive-forge tree-sha: --json is not supported for this verb, only the plain sha");
+    }
     let (owner, name) = client.owner_repo()?;
     // Try branch first; the bash helper silently treats failure as
     // "not a branch, use the reference as a commit sha directly".