docs(multi-user): server-wide settings writes are admin-only

api-reference gains a Settings section (GET/PUT /api/settings, the model
config, the case order and PUT /api/config, with the 403 FORBIDDEN a non-admin
gets in multi-user mode). The Multi-User Mode wiki page explains what a regular
user's App Settings save does now, Settings-Reference links it, the plan's
Settings row is marked implemented, and CLAUDE.md notes the gate for the
Multi-user paragraph and for anyone adding a settings write.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/wiki/Multi-User-Mode.md

@@ -60,6 +60,27 @@ Admins see everything.
 Ownership threads through every list endpoint, the session lookup helper, the WebSocket
 layer, and file previews. A user cannot address another user's session even by id.
 
+## Server-wide settings are admin only
+
+There is one set of server settings (`~/.codeman/settings.json`) for everyone: the feature
+switches, the run mode, respawn presets, the case order, the Cloudflare tunnel, the default
+models. Every user can **read** them, but only an **admin** can change them. For a regular
+user the settings write routes answer `403 FORBIDDEN` (see the
+[HTTP API](HTTP-API) and [`docs/api-reference.md`](https://github.com/Ark0N/Codeman/blob/master/docs/api-reference.md)).
+
+In the browser this means:
+
+- **App Settings → Save** still keeps a regular user's per-device settings (skin, fonts,
+  header buttons, keyboard bar and the rest of the per-device keys) on that device. If they
+  also changed a server-wide setting, one notice says it can only be changed by an admin,
+  and the setting keeps the server's value.
+- A regular user's run-mode pick and respawn presets are kept in that browser and not sent
+  to the server, and their last used case is not recorded server-wide. What an admin set
+  still loads on the next visit.
+- Reordering cases and switching the tunnel on or off are admin actions.
+
+Per-user server settings are not part of this version.
+
 ## Safer defaults for regular users
 
 Non-admins get tighter defaults, and lifting them is an explicit per-user grant:

docs/wiki/Settings-Reference.md

@@ -29,6 +29,10 @@ The practical rule: **appearance and input are per device, behaviour is shared.*
 did not follow you, it is in one of the first two rows, and you change it again on that
 device.
 
+In [Multi-User Mode](Multi-User-Mode) the server's settings are shared by every user, so
+only an **admin** can change them. A regular user's **Save** keeps their per-device settings
+as usual and tells them that server-wide settings can only be changed by an admin.
+
 ## App Settings
 
 ### Updates