chore(mongo): reduce overlapping volume mounts to single /data mount

[wax911]

Closes #504.

Removes redundant /data/db and /data/configdb volume mounts. MongoDB's default dbPath and config DB path are subdirectories of /data, so the single mount covers all persistence needs.

[wax911]

This needs another pass before merge.

The intent from #504 was to remove ambiguity, but switching to only mongo-data:/data is not sufficiently validated for the official mongo image. The official docker-library Mongo Dockerfile template explicitly declares:

VOLUME /data/db /data/configdb

Source: https://github.com/docker-library/mongo/blob/master/Dockerfile-linux.template

Because the image declares exact child volume paths, a parent /data mount may not prevent Docker from creating anonymous volumes for /data/db and /data/configdb. That would defeat the persistence simplification and make backup/restore semantics less obvious, not more obvious.

Safer options:

1. Remove only the parent /data mount and keep exact mounts for /data/db and /data/configdb.
2. Use separate named volumes for /data/db and /data/configdb.
3. Keep this PR's single /data approach only if runtime validation proves no anonymous child volumes are created for this image.

Also remove .slim/deepwork/issues-500-505.md from this PR. The #505 direction now lives in the issue comment and should not be duplicated inside an unrelated Mongo volume PR.