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

core/schema/chats.go

@@ -1900,6 +1900,58 @@ type ChatsToolsPanel struct {
 	// that no add-on serves in this chat now: the add-on is stopped, off for
 	// the chat, not granted by its agent, or cannot run.
 	Fallbacks []ChatsToolFallback `json:"fallbacks,omitempty"`
+	// Memory says whether memory works in this chat and, when it does not,
+	// which level turned it off and where to turn it on again.
+	Memory ChatsMemoryState `json:"memory"`
+}
+
+// ChatsMemoryState is whether memory works in one chat. The narrowest level
+// that is off wins: this chat (a private chat), the agent of the chat, your
+// memory switch, then the server.
+type ChatsMemoryState struct {
+	// On is true when the chat reads and may save notes.
+	On bool `json:"on" example:"false"`
+	// Code names the level that is off: memory_off_chat, memory_off_agent,
+	// memory_off_user or memory_off_files. Absent when on.
+	Code string `json:"code,omitempty" example:"memory_off_chat"`
+	// BlockedBy is who holds that switch: chat, agent, user or server.
+	BlockedBy string `json:"blocked_by,omitempty" example:"chat"`
+	// Reason is an English sentence for logs; the interface words it by Code.
+	Reason string `json:"reason,omitempty"`
+	// Fix says where to turn memory on again: kind open_tools_menu,
+	// open_memory_settings, open_agent or open_server_setting.
+	Fix *ChatsMemoryFix `json:"fix,omitempty"`
+}
+
+// ChatsMemoryFix points at the one place that turns memory on again.
+type ChatsMemoryFix struct {
+	Kind   string `json:"kind" example:"open_memory_settings"`
+	Target string `json:"target" example:"memory"`
+	Field  string `json:"field,omitempty"`
+}
+
+// ChatsMemorySettings is your memory choices.
+type ChatsMemorySettings struct {
+	// Enabled is memory On or Off for all your chats and agents.
+	Enabled bool `json:"enabled" example:"true"`
+	// EnabledSet is true once you chose. Before that memory is on, unless you
+	// had disabled the Memory add-on to stop it.
+	EnabledSet bool `json:"enabled_set" example:"false"`
+	// SaveMode is how a note is saved: ask, auto or never.
+	SaveMode string `json:"save_mode" example:"ask"`
+	// SaveModeSet is true once you chose in this setting.
+	SaveModeSet bool `json:"save_mode_set" example:"false"`
+	// Provider is what serves memory: builtin.
+	Provider string `json:"provider" example:"builtin"`
+	// Available is false when the server has no files, which notes need.
+	Available bool `json:"available" example:"true"`
+}
+
+// ChatsMemoryRequest changes your memory choices. A field left out stays as
+// it is.
+type ChatsMemoryRequest struct {
+	Enabled  *bool   `json:"enabled,omitempty" example:"false"`
+	SaveMode *string `json:"save_mode,omitempty" example:"ask"`
 }
 
 // ChatsToolFallback is one built-in tool whose replacing add-on cannot serve