hive-forge: drop boilerplate # Errors from pure-GET verbs (mara on #827, option A)

mara: 'those comments seem very redundant'. true — the 16 pure-GET
verbs all got the same 'transport error + stdout I/O' boilerplate,
which just restates the Result<()> contract that's trivially
derivable from the type.

dropped # Errors from: assign, branches, close, comment_show,
comments, diff, issue, labels, lint, list, milestone, pr,
pr_reviews, subscription, timeline, tree_sha, view (17 files).

kept on the 7 verbs that have a non-Forgejo failure surface worth
documenting:
- comment, comment_edit, issue_create, issue_edit — body input I/O
  via --body-file / stdin
- pr_create — body input + --push shellout to git
- attach::run_issue, attach::run_comment — explicit bail! on
  missing file

net: 23 verbs touched in the original PR → 17 trimmed back to
no-doc, 6 kept (with the 7th call being attach::run_comment in the
same file). 38 tests still pass.

hive-forge/src/verbs/diff.rs

@@ -30,11 +30,6 @@ pub struct Args {
     full: bool,
 }
 
-/// # Errors
-///
-/// Propagates any transport error from the Forgejo REST call
-/// (network unreachable, 4xx/5xx response, token missing/invalid)
-/// and any I/O error from writing the response to stdout.
 pub fn run(client: &Client, args: Args) -> Result<()> {
     let repo = client.repo();
     let diff = client.get_text(&format!("/repos/{repo}/pulls/{}.diff", args.number), "text/plain")?;