feat(agent): Agent 工作台 - 计划插话记忆、统一模型选择器并修复摘要与视频入库

将计划清单、运行中插话和个人记忆接入云端 Agent；全站模型选择器统一为左右二级菜单。画布摘要按预算截断不再整轮拒绝，首页视频未知宽高可入库。README 补充贡献者 morrow。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/app/cloud_agent_continuation_test.go

@@ -0,0 +1,77 @@
+package app
+
+import (
+	"strings"
+	"testing"
+
+	"infinite-canvas/backend/internal/model"
+)
+
+func TestCloudAgentContinuationReplySplitsFactsFromAssistantText(t *testing.T) {
+	task := &model.Task{Status: model.TaskStatusSucceeded, ResultJSON: `{"text":"已完成"}`}
+	run := &CloudAgentRun{
+		ID:     "ag1",
+		Status: "failed",
+		Events: []CloudAgentEvent{
+			{Type: "assistant_message", Payload: map[string]any{"text": "先看画布"}},
+			{Type: "tool_completed", Payload: map[string]any{"toolName": "canvas_get_state", "nodeId": "n1"}},
+			{Type: "run_failed", Payload: map[string]any{"reason": "cancelled"}},
+		},
+	}
+	reply, context, err := cloudAgentContinuationReply(task, run)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if reply != "先看画布" {
+		t.Fatalf("reply 应是上一轮 assistant 正文，got %q", reply)
+	}
+	if context == "" {
+		t.Fatal("失败轮次必须留下收束摘要")
+	}
+	if strings.Contains(reply, "上一轮已结束") || strings.Contains(reply, "canvas_get_state") {
+		t.Fatal("摘要不能拼进 assistant 历史")
+	}
+	if strings.Contains(context, "canvas_get_state") || strings.Contains(context, `"event"`) {
+		t.Fatalf("摘要不得把工具流水当成本轮目标：%s", context)
+	}
+	if !strings.Contains(context, "上一轮已结束（failed）") || !strings.Contains(context, "当前用户消息") {
+		t.Fatalf("失败摘要不对：%s", context)
+	}
+}
+
+func TestCloudAgentContinuationOmitsQuietCompletedTurns(t *testing.T) {
+	task := &model.Task{Status: model.TaskStatusSucceeded, ResultJSON: `{"text":"好"}`}
+	run := &CloudAgentRun{
+		Status: "completed",
+		Events: []CloudAgentEvent{
+			{Type: "assistant_message", Payload: map[string]any{"text": "好"}},
+			{Type: "tool_completed", Payload: map[string]any{"toolName": "canvas_get_state"}},
+		},
+	}
+	reply, context, err := cloudAgentContinuationReply(task, run)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if reply != "好" || context != "" {
+		t.Fatalf("安静完成的一轮不应再塞执行流水：reply=%q context=%q", reply, context)
+	}
+}
+
+func TestCloudAgentContinuationKeepsSubmittedTaskIDs(t *testing.T) {
+	task := &model.Task{Status: model.TaskStatusSucceeded}
+	run := &CloudAgentRun{
+		Status: "completed",
+		Events: []CloudAgentEvent{
+			{Type: "assistant_message", Payload: map[string]any{"text": "已提交"}},
+			{Type: "generation_task_created", Payload: map[string]any{"taskId": "task-1"}},
+			{Type: "tool_completed", Payload: map[string]any{"result": map[string]any{"taskId": "task-2", "taskSubmitted": true}}},
+		},
+	}
+	_, context, err := cloudAgentContinuationReply(task, run)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(context, "task-1") || !strings.Contains(context, "task-2") || !strings.Contains(context, "不要重发") {
+		t.Fatalf("已提交任务应留下防重发提示：%s", context)
+	}
+}