docs(admin): rewrite deleted files configuration chapter

[joshtrichards]

☑️ Resolves

Rewrites the admin-facing trash bin / deleted files chapter to align it with the current files_trashbin implementation.

The existing chapter is outdated and incomplete: it does not document the trash-bin size mechanism (50% of remaining quota space, or available filesystem space for accounts without a quota), omits trashbin:size, trashbin:cleanup, and trashbin:restore, and describes the retention-policy values (auto, D1, auto, auto, D2, D1, D2, and bare numeric values) imprecisely, particularly regarding space-triggered cleanup and D1/D2 clamping. Background-job cadence and which policies trigger a time-based expiration pass were also not documented.

Changes:

• Policy Configuration: explains the semantics of each trashbin_retention_obligation value, including its interaction with space-triggered cleanup.
• Trash-bin Size / Interaction with Quotas: adds occ trashbin:size, global versus per-account precedence, and the 50%-of-remaining-quota default, with available filesystem space used for accounts without a quota.
• Background Jobs: explains the interval, batching behavior, and which policies trigger a time-based expiration pass.
• Manual Expiration, Removing All Trashed Items, and Restoring All Trashed Items: documents trashbin:expire, trashbin:cleanup, and trashbin:restore, including --all-users versus user-ID handling and the --since, --until, --scope, and --dry-run options.
• Expands the introduction to cover restore-location fallback and interaction with the Versions app.

The documented behavior was checked directly against the relevant implementation rather than carried over from the previous documentation.

Separately, a minor wording issue was identified in the occ trashbin:expire output for the disabled-retention case. That's a code fix, not a docs one, and will be addressed separately.

🖼️ Screenshots

See generated preview when CI completes.

✅ Checklist

• I have built the documentation locally and reviewed the output
• Screenshots are included for visual changes
• I have not moved or renamed pages (or added a redirect if I did)
• I have run codespell or similar and addressed any spelling issues

[kesselb]

Thanks a lot!

I'd just a had a chat about this page the other day because some of the information are outdated.

Louis reworked https://docs.nextcloud.com/server/stable/admin_manual/configuration_server/config_sample_php_parameters.html#deleted-items-trash-bin recently.

What do you think about moving the enhanced documention for trashbin_retention_obligation over to the config.sample.php and set a backlink here?