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/servers/api/users/manage-users.ts

@@ -2,7 +2,6 @@ import type { Handler } from 'hono';
 import { getUsers, getUserById, updateUser, deleteUser, USER_ROLES, OWNER_USER_ID } from 'officerdb';
 import type { UserRole } from 'officerdb';
 import * as errors from '@@/custom-errors';
-import { OS_USERS_ENABLED } from '@@/os-user';
 import { deprovisionOsAccount } from '@@/os-user-deprovision';
 import { DATA_PATH } from '@@/data-path';
 
@@ -56,9 +55,6 @@ export const listUsersHandler: Handler = async function (ctx) {
     roles: USER_ROLES,
     assignableRoles: USER_ROLES.filter((r) => r !== 'Super Admin'),
     ownerId: OWNER_USER_ID,
-    // So the UI offers the Linux-account controls only where they can work. On a host without the feature
-    // they would be a button that always reports the same refusal.
-    osUsersEnabled: OS_USERS_ENABLED,
   });
 };
 
@@ -119,7 +115,7 @@ export const deleteUserHandler: Handler = async function (ctx) {
   // first and a failed deprovision is unrecoverable through the UI: no row, no osUser, nothing to retry
   // against. Keeping the account on failure is also the safer half of the trade — an account that still
   // exists is inert, whereas a freed uid whose files still carry it is the hazard itself.
-  if (OS_USERS_ENABLED && existing.osUser) {
+  if (existing.osUser) {
     const deprovisioned = await deprovisionOsAccount({ email: existing.email, osUser: existing.osUser });
     if (!deprovisioned.ok) {
       // Loud on purpose. A missing Docker install warns into a log; this one names the account, the stage