Replace individual env var add/edit/delete with a single bulk save
endpoint. The UI now shows a textarea with KEY=VALUE lines. On save,
all existing env vars are deleted and the full submitted set is
inserted.
- Replace HandleEnvVarAdd, HandleEnvVarEdit, HandleEnvVarDelete with
HandleEnvVarSave
- Collapse 3 routes into single POST /apps/{id}/env
- Template uses textarea instead of per-row edit/delete forms
- No individual env var IDs exposed in the UI
- Extract parseEnvPairs helper to keep cyclomatic complexity low
- Use strings.SplitSeq per modernize linter
- Update tests for new bulk save behavior
closes #156
closes #163
Change route patterns in routes.go from /env-vars to /env and update
edit/delete form actions in app_detail.html to match. The add form
already used /env and was correct.
Update test route setup to match the new /env paths.
Closes#156