In `@beeminder.go`:
- Around line 645-649: UpdateGoalDeadline constructs the API path with the raw
goalSlug which can break for spaces/special characters; mirror FetchGoal by
applying url.PathEscape to goalSlug before building apiURL so the PUT path is
properly escaped (update the UpdateGoalDeadline function to call
url.PathEscape(goalSlug) when formatting apiURL).

In `@main.go`:
- Around line 1206-1236: The parseTimeToDeadlineOffset function currently uses
if hour > 6 to decide wrapping, which leaves 6:01–6:59 AM as positive offsets
exceeding Beeminder's +21600 limit; update the wrap condition in
parseTimeToDeadlineOffset to treat any time after 6:00 AM as wrapping (i.e., if
hour > 6 OR hour == 6 and minute > 0) so offsets for 6:01–6:59 become negative
via offset = offset - 24*3600; keep 6:00 AM (hour==6 && minute==0) as the
maximum positive 21600.

In `@beeminder.go`:
- Around line 672-675: The non-200 response handling in the unnamed block
discards the io.ReadAll error which can mask failures; update this block to read
resp.Body into body and check the error from io.ReadAll, returning a formatted
error that includes both the HTTP status and either the body content (if read
succeeded) or the read error (if read failed), mirroring the pattern used in
CreateCharge and FetchGoalRawJSON so callers receive clear, explicit failure
information.

In `@main.go`:
- Around line 1247-1252: The deadline command's flag parsing uses deadlineFlags
:= flag.NewFlagSet(...) and calls deadlineFlags.Parse(os.Args[2:]) but doesn't
handle flag.ErrHelp or return the same exit code as other commands; update the
Parse error handling to mirror next/add/view: if err == flag.ErrHelp then print
deadlineFlags.Usage() and exit 0, else print the flag error (or usage) and exit
2. Ensure you reference deadlineFlags.Parse, flag.ErrHelp, and the yes/yesShort
flags so the code shows usage on -h and returns exit code 2 for parse errors.