feat(memory): add a Memory On/Off switch and private chats

Memory now has one switch, On or Off, in the Memory tab of the account
settings. Off means nothing from the notes is put in the prompt, the
model has no memory skill, tool or note kind, nothing is proposed or
saved (also by triggers and other runs that start by themselves), and
the model is told in one line that memory is off. The notes stay and can
still be read, exported and deleted.

A chat can be private: the Memory row of its Tools menu is the memory
switch group, stored with the chat. The narrowest level wins: chat,
agent, person, server. A saved agent cannot widen the choice of the
person. The tools list says which level is off (memory.code, blocked_by,
fix); the chat shows a chip and one line, and the agent form shows the
person's switch as a read-only line.

New API: GET and PUT /api/chats/memory for the switch and the save level,
and GET /api/chats/memory/export for a zip of the notes. The Memory tab
gains the switch, the three save levels, Export and Forget everything.

Assisted-by: Claude:claude-sonnet-5-5

docs/content/features/chats.md

@@ -1343,6 +1343,7 @@ it off, so a chat that never touches the menu works as before:
 | **Sub-agents** | `subagents` | `spawn_agent` |
 | **Saved agents** | `saved_agents` | `list_agents` and the `agent` argument of `spawn_agent` (opt-in) |
 | **Triggers** | `triggers` | `propose_trigger`, `list_triggers`, `update_trigger` and `delete_trigger` |
+| **Memory** | `memory` | Your notes: the model reads them before it answers and may save new ones (see [Memory](/features/short-memory/)). Switch it off to make the chat private: it neither reads nor saves memory |
 | **Suggested changes** | `changes` | `propose_change` and `revert_change`: a model asks to change your notes, an agent profile, a skill, a page or the dashboard, and you confirm (see [change proposals](/features/addons/#change-proposals-from-chats)); for memory notes only, you can choose in your account settings to have them saved at once with an Undo, or never (see [Memory](/features/short-memory/#choose-how-a-note-is-saved)) |
 
 ```bash

docs/content/features/short-memory.md

@@ -33,6 +33,54 @@ There are three kinds of notes, each in the Memory folder of your files:
 An index has at most 40 lines and 2 KiB. All indexes of a turn together have at most 6 KiB.
 The details of a topic sit in a file next to the index.
 
+## Turn memory off
+
+Memory has one switch, **On** or **Off**, at the top of the **Memory** tab of your
+account settings (**Your settings**, then **Memory**). It is on until you turn it off.
+
+When memory is off:
+
+- Nothing from your notes is put in the prompt, in any chat, agent, trigger or run that
+  starts by itself.
+- The model has no memory tool or skill: it cannot read a note, propose one or save one.
+- The model is told in one line that memory is off. If you ask it to remember something,
+  it says that memory is off and that you can turn it on again.
+- Your notes stay where they are. You can still read, edit, export and delete them on the
+  **Memory** tab while memory is off.
+
+The narrowest level wins, and a wider level never overrides a narrower one:
+
+1. **This chat** is private (see below).
+2. **The agent** of the chat turns memory off in its **Tools** list.
+3. **Your switch** in the account settings is off.
+4. **The server** has files off, because notes are files.
+
+A saved agent cannot widen your choice: with your switch off, an agent that is allowed to
+save notes still reads and saves none. The agent form shows "Memory is off in your
+settings" as a read-only line.
+
+### Private chat
+
+In the **Tools** menu of a chat, the **Memory** row has a switch. Turn it off to make the
+chat private: it neither reads nor saves memory. The server remembers it for that chat,
+and a chip "Private chat" and a line in the Tools menu say so. Your other chats are not
+affected, and notes saved earlier are not removed. It is the same switch as the group
+`memory` of `PUT /api/chats/{id}/builtins`; `GET /api/chats/{id}/tools` has a `memory`
+object ({`on`, `code`, `blocked_by`, `fix`}) that names the level that is off.
+
+### Export and forget
+
+On the **Memory** tab, **Export** downloads your notes as a zip file
+(`GET /api/chats/memory/export`). **Forget everything** moves the notes to the Trash after
+you confirm; you can restore them from Files. Both work while memory is off.
+
+### The API
+
+`GET /api/chats/memory` reads `{enabled, enabled_set, save_mode, save_mode_set, provider,
+available}` and `PUT /api/chats/memory` with `{enabled, save_mode}` changes them. The server
+keeps them with your other settings, so every frontend of a cluster reads the same answer.
+Before you choose, memory is on, unless you had disabled the old Memory add-on to stop it.
+
 ## Saving and forgetting
 
 When you ask the model to remember something, it calls `propose_change`. By default