Fix red develop a17d612dfd02

The merge lane found `develop` red at `a17d612dfd02451b08991c81dd34e567f226537f` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `mirror-trees-strict` - `community-edition-tooling-suite` The whole gate log: artifact `12751` on lane task 11642. Make `develop` pass its full gate again. Open a PR as usual: the merge lane merges a PR that fixes some of these and adds no failure even while `develop` is red.

Fixed red develop: html_text.py (imported only by cloud-only modules) was a CE-tree orphan; named it in features.toml system_mail. Mirror trees + CE tooling suite green locally, quick gate green. PR #7449 queued to merge lane. Memory: none applied.