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/handler/api/v1/email_channel_migration_handler.go

@@ -0,0 +1,78 @@
+package v1
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/gochat/gochat/internal/model"
+	"github.com/gochat/gochat/internal/service"
+	"github.com/gochat/gochat/pkg/response"
+)
+
+// EmailChannelMigrationHandler handles account-scoped email channel migration endpoints.
+// Reference: Chatwoot api/v1/accounts/:account_id/email_channel_migrations — create-only
+// endpoint for initiating migration of an email channel from one inbox to another.
+type EmailChannelMigrationHandler struct {
+	svc *service.EmailChannelMigrationService
+}
+
+// NewEmailChannelMigrationHandler creates a new EmailChannelMigrationHandler with service injection.
+func NewEmailChannelMigrationHandler(svc *service.EmailChannelMigrationService) *EmailChannelMigrationHandler {
+	return &EmailChannelMigrationHandler{svc: svc}
+}
+
+// Create initiates a new email channel migration from one inbox to another.
+// POST /api/v1/accounts/:account_id/email_channel_migrations
+func (h *EmailChannelMigrationHandler) Create(c *gin.Context) {
+	accountID := getAccountID(c)
+	if accountID == 0 {
+		response.AbortWithStatusError(c, http.StatusBadRequest, response.ErrBadRequest, "invalid account_id")
+		return
+	}
+
+	var req struct {
+		InboxID       uint `json:"inbox_id" binding:"required"`
+		TargetInboxID uint `json:"target_inbox_id" binding:"required"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.AbortWithStatusError(c, http.StatusBadRequest, response.ErrValidation, err.Error())
+		return
+	}
+
+	migration := &model.EmailChannelMigration{
+		AccountID:       accountID,
+		InboxID:         req.InboxID,
+		TargetInboxID:   req.TargetInboxID,
+		MigrationStatus: "pending",
+	}
+
+	if svcErr := h.svc.Create(c.Request.Context(), migration); svcErr != nil {
+		handleServiceError(c, svcErr)
+		return
+	}
+	response.Created(c, migration)
+}
+
+// List retrieves all email channel migrations for the current account.
+// GET /api/v1/accounts/:account_id/email_channel_migrations
+func (h *EmailChannelMigrationHandler) List(c *gin.Context) {
+	accountID := getAccountID(c)
+	if accountID == 0 {
+		response.AbortWithStatusError(c, http.StatusBadRequest, response.ErrBadRequest, "invalid account_id")
+		return
+	}
+
+	migrations, err := h.svc.ListByAccount(c.Request.Context(), accountID)
+	if err != nil {
+		handleServiceError(c, err)
+		return
+	}
+	response.OK(c, migrations)
+}
+
+// RegisterEmailChannelMigrationRoutes registers email channel migration routes on the given router group.
+func RegisterEmailChannelMigrationRoutes(g *gin.RouterGroup, h *EmailChannelMigrationHandler) {
+	g.POST("/", h.Create)
+	g.GET("/", h.List)
+}