Reorganize repo: backend/, deploy/, docs/ layout + AGENTS.md

Restructure the monorepo into clear top-level directories:
- backend/: Go module root (cmd, internal, pkg, configs, migrations,
  docs/swagger, scripts, tests, go.mod, Makefile, .air.toml)
- deploy/: Docker (Dockerfile, docker-compose*), quickstart, fluentd
- docs/: project documentation + reports/ (moved from repo root)
- AGENTS.md: new AI coding-agent guide at repo root

Update all references to the new layout:
- Dockerfile: COPY backend/go.mod, COPY backend/ (context = repo root)
- docker-compose files: context ../.., dockerfile deploy/docker/Dockerfile,
  env_file ../../.env, volume mounts ../../backend:/app
- deploy/quickstart/compose.yaml: dockerfile deploy/docker/Dockerfile
- CI: working-directory: backend for go commands, file deploy/docker/Dockerfile,
  coverage path backend/coverage.out, health_check backend/scripts/
- backend/Makefile: docker target uses -f ../deploy/docker/Dockerfile ../
- README: architecture tree, quickstart, config paths updated

Move root stray scripts (rename_models.*, run_m11_tests.sh, verify_build.sh,
gorm_bool_main.go) to backend/scripts/legacy/. All moves via git mv to
preserve history. Build, vet, SQLite tests, and docker compose config verified.

backend/internal/service/copilot_response_worker.go

@@ -0,0 +1,46 @@
+package service
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"sync"
+
+	"github.com/gochat/gochat/internal/model"
+	"github.com/gochat/gochat/internal/worker"
+)
+
+const TaskTypeCaptainCopilotResponse = "captain:copilot_response"
+
+type captainCopilotResponseJob struct {
+	AccountID       uint   `json:"account_id"`
+	UserID          uint   `json:"user_id"`
+	ConversationID  uint   `json:"conversation_id,omitempty"`
+	CopilotThreadID uint   `json:"copilot_thread_id"`
+	MessageID       uint   `json:"message_id"`
+	Message         string `json:"message,omitempty"`
+}
+
+var copilotResponseRegistrations sync.Map
+
+func RegisterCopilotResponseJobs(wp *worker.WorkerPool, svc *CopilotService) {
+	if wp == nil || svc == nil {
+		return
+	}
+	if _, loaded := copilotResponseRegistrations.LoadOrStore(wp, struct{}{}); loaded {
+		return
+	}
+	wp.Register(TaskTypeCaptainCopilotResponse, svc.performCopilotResponseJob)
+}
+
+func (s *CopilotService) performCopilotResponseJob(ctx context.Context, job *model.BackgroundJob) error {
+	var payload captainCopilotResponseJob
+	if err := json.Unmarshal(job.Payload, &payload); err != nil {
+		return fmt.Errorf("unmarshal captain copilot response job: %w", err)
+	}
+	if payload.AccountID == 0 || payload.UserID == 0 || payload.CopilotThreadID == 0 || payload.MessageID == 0 {
+		return fmt.Errorf("invalid captain copilot response job payload: %#v", payload)
+	}
+	_, err := s.GenerateCopilotResponseByAccount(ctx, payload.AccountID, payload.UserID, payload.CopilotThreadID, payload.ConversationID, payload.MessageID, payload.Message)
+	return err
+}