per-user linux accounts are not optional any more

OFFICER_OS_USERS is gone. The platform behaves as it always would have with the
flag on, and there is nothing to enable.

Six conditionals, five of which were dead weight — provisionOsAccount,
deprovisionOsAccount and the create/delete paths each opened with an early
"not enabled on this server" return, and the API told the frontend whether to
render the Linux controls at all. Those go, along with the 'disabled'
DeprovisionResult stage, which nothing can produce now.

The sixth is the one with teeth. assertSecretsClosed opened with
`if (!OS_USERS_ENABLED) return`, described in its own comment as "a no-op when
the feature is off, so an existing install is unaffected until the owner opts
in". It is now unconditional: the server refuses to boot while any .env in the
project root is group- or world-readable. A member's shell reading .env and
printing JWT_SECRET was confirmed exploitable when this check was written, and a
prerequisite that only holds when somebody remembers to set a variable is not a
prerequisite.

Nothing to remove on the environment side — the flag was never in .env.example
or in the setup script.

Not typechecked: node_modules is empty in this tree and installs are frozen, so
tsgo could not run. All six files parse under `bun build --no-bundle`, and the
changes are deletions of dead branches plus one removed early return. Formatted
with prettier 3.9.6 via bunx rather than the pinned resolution, for the same
reason; its one unrelated reformat was reverted by hand.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/apps/officer-web/Screens/Dashboard/Settings/UserManagement/UsersSection.tsx

@@ -32,8 +32,6 @@ type ManagedUser = {
 
 type UsersResponse = {
   users: ManagedUser[];
-  /** False on a host without per-user Linux accounts, where those controls would only ever refuse. */
-  osUsersEnabled: boolean;
   /** Every role, for displaying the owner's own value. */
   roles: string[];
   /** Roles the server will accept in a write. Excludes the owner role — both write paths refuse it. */
@@ -183,7 +181,7 @@ export const UsersSection = () => {
               {/* Create or repair the Linux side. Offered for anyone lacking an account (backfill) and for
                   anyone who has one (retry after fixing a host problem, or replace their key) — the
                   underlying operation is idempotent, so there is no state where pressing it is wrong. */}
-              {data.osUsersEnabled && !user.isOwner && (
+              {!user.isOwner && (
                 <Button
                   variant="ghost"
                   size="icon"