hive-forge: add # Errors docs on every verb's pub fn run (closes #816)

systemic gap argus flagged on PR #798 (timeline verb). every `pub fn
run` in hive-forge/src/verbs/*.rs lacked a `# Errors` block —
violates Rust API guidelines + obscures the failure surface for
operators reading the source.

uniform doc per verb category:
- pure GET + print verbs: "transport error from the Forgejo REST call
  + I/O error from stdout"
- body-from-file verbs (comment/comment_edit/issue_create/issue_edit/
  pr_create): adds 'I/O error from --body-file/stdin input'
- file-upload verbs (attach-issue, attach-comment): adds 'file
  read/exist check'
- pr_create: also mentions the --push shellout

23 `pub fn run` signatures touched. no behaviour change; pure
documentation sweep. cargo test green (38 tests).

hive-forge/src/verbs/attach.rs

@@ -26,6 +26,12 @@ pub struct CommentArgs {
     file: PathBuf,
 }
 
+/// # Errors
+///
+/// Returns an error if the input file doesn't exist or can't be
+/// read. 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 browser download URL to stdout.
 pub fn run_issue(client: &Client, args: IssueArgs) -> Result<()> {
     if !args.file.is_file() {
         bail!(
@@ -42,6 +48,12 @@ pub fn run_issue(client: &Client, args: IssueArgs) -> Result<()> {
     Ok(())
 }
 
+/// # Errors
+///
+/// Returns an error if the input file doesn't exist or can't be
+/// read. 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 browser download URL to stdout.
 pub fn run_comment(client: &Client, args: CommentArgs) -> Result<()> {
     if !args.file.is_file() {
         bail!(