chore: apply the Frappe version-16 migration guide items

[av-dev2]

Applies the items from frappe's Migrating to version 16 guide that csf_tz still owed. Each commit covers one file.

Changes

• Default list ordering. v16 sorts by creation desc instead of modified desc and no longer indexes modified. All 39 non-child DocTypes that still declared sort_field: "modified" now sort by creation, matching frappe core (98 of its 101 core DocTypes). Child tables are untouched — they ignore sort_field.
• Desktop apps screen. v16 only lists apps that declare add_to_apps_screen, so csf_tz never appeared. Added with the app logo and the /desk/tanzania route; frappe.apps.get_apps() now returns it beside ERPNext and Frappe HR.
• Workspace ownership. v16 workspaces carry an app field used by the new sidebar and desktop; the Tanzania workspace had none.

The remaining guide items were audited and needed no change here: the removed translation APIs, value_cache, GeoIP, site_cache, bleach, Transaction Log, the POST-only endpoints and sendmail(now=True) are not used; has_permission hooks are not registered; Time field defaults already use "Now"; and get_valid_columns() is only called on DocTypes without virtual fields. The guide's other applicable items are covered by the compatibility, client-script and reports pull requests.

Note on review order

The sort_field change is the one with visible user impact: list views default to newest-created rather than most-recently-modified. It is the guide's recommended migration, and it is isolated in this pull request so it can be accepted or deferred on its own.

Verification

bench migrate is clean and the full suite (631 test cases) passes with these changes applied.