Feature: Offline device history with delete and remote uninstall

Persist every device that has ever logged in to the Go server in a small
JSON store (devices.json, overridable with YAMA_DEVICES_FILE and capped by
YAMA_DEVICES_MAX, default 1000 newest). The store follows the users.json
convention: atomic temp-file write with fsync and rename, a 500 ms debounce
for bursts of reconnects, first_seen preserved across logins, and pruning
that evicts offline records before devices that are still connected.
Devices connected at shutdown are stamped offline before the final flush so
last_seen stays accurate across restarts.

The server advertises an offlineDevices capability and device_list now
appends historical devices that are not online, marked with online:false and
last_seen. The web UI shows an Offline checkbox after Total/Showing (state
kept in localStorage), renders offline cards dimmed and dashed, and always
lists them in the screen-wall sidebar. Older servers without the capability
keep the online-only list.

Grid and List cards gain a delete button after the terminal button, admin
only, behind a confirmation dialog. Deleting an offline device removes its
history record; deleting an online device first sends the single-byte
TOKEN_UNINSTALL command (matching the MFC OnOnlineUninstall flow) and then
removes the record too, so the device does not come back as a dead offline
entry. The agent's own disconnect then runs the existing cleanup path:
screen and terminal sub-connections are closed, the hub entry is removed,
and browsers receive device_offline to release their watch sets, wall
sessions, and stream references. Wall mode exposes no delete action.

Tests cover history persistence/pruning/recovery, offline ordering, the
device_list merge, and all three delete outcomes (offline removal, online
uninstall with a single 0x3F byte, and viewer rejection).

Co-Authored-By: deepseek-flash

server/go/web/device_list_test.go

@@ -0,0 +1,53 @@
+package web
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/yuanyuanxiang/SimpleRemoter/server/go/connection"
+	"github.com/yuanyuanxiang/SimpleRemoter/server/go/devicehistory"
+	"github.com/yuanyuanxiang/SimpleRemoter/server/go/hub"
+)
+
+func TestListDevicesWithOffline(t *testing.T) {
+	h := hub.New()
+	hist, err := devicehistory.Open(filepath.Join(t.TempDir(), "devices.json"), 100, nil)
+	if err != nil {
+		t.Fatalf("Open history: %v", err)
+	}
+	t.Cleanup(func() { _ = hist.Close() })
+	h.Subscribe(hist)
+
+	h.Register(&hub.Device{ID: "online", Name: "Online"},
+		&connection.Context{RemoteAddr: "10.0.0.1:1000"})
+	h.Register(&hub.Device{ID: "gone", Name: "Gone"},
+		&connection.Context{RemoteAddr: "10.0.0.2:1000"})
+	h.Unregister("gone")
+
+	wh := &wsHub{devices: h, history: hist}
+	got := wh.listDevicesWithOffline()
+	if len(got) != 2 {
+		t.Fatalf("devices = %d, want 2 (1 online + 1 offline)", len(got))
+	}
+	if got[0].ID != "online" || !got[0].Online {
+		t.Fatalf("first = %+v, want online device", got[0])
+	}
+	if got[1].ID != "gone" || got[1].Online {
+		t.Fatalf("second = %+v, want offline device", got[1])
+	}
+	if got[1].LastSeen == 0 {
+		t.Fatal("offline device missing last_seen")
+	}
+}
+
+func TestListDevicesWithoutHistoryIsOnlineOnly(t *testing.T) {
+	h := hub.New()
+	h.Register(&hub.Device{ID: "online", Name: "Online"},
+		&connection.Context{RemoteAddr: "10.0.0.1:1000"})
+
+	wh := &wsHub{devices: h}
+	got := wh.listDevicesWithOffline()
+	if len(got) != 1 || got[0].ID != "online" {
+		t.Fatalf("devices = %+v, want just the online device", got)
+	}
+}