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/contact_merge_handler_test.go

@@ -0,0 +1,121 @@
+package v1
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/gochat/gochat/internal/model"
+	"github.com/gochat/gochat/internal/repository"
+	"github.com/gochat/gochat/internal/service"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/suite"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+	"gorm.io/gorm/logger"
+)
+
+type ContactMergeHandlerTestSuite struct {
+	suite.Suite
+	db      *gorm.DB
+	handler *ContactMergeHandler
+
+	account  *model.Account
+	contact1 *model.Contact
+	contact2 *model.Contact
+}
+
+func (s *ContactMergeHandlerTestSuite) SetupSuite() {
+	gin.SetMode(gin.TestMode)
+	db, err := gorm.Open(sqlite.Open("file::memory:"), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	s.Require().NoError(err)
+	s.Require().NoError(db.AutoMigrate(&model.Account{}, &model.Contact{}, &model.ContactInbox{}, &model.Conversation{}, &model.Message{}, &model.ContactNote{}, &model.Note{}))
+	s.db = db
+
+	mergeRepo := repository.NewContactMergeRepo(db)
+	mergeSvc := service.NewContactMergeService(mergeRepo, db)
+	s.handler = NewContactMergeHandler(mergeSvc)
+
+	s.account = &model.Account{Name: "test-merge-account"}
+	s.db.Create(s.account)
+	s.contact1 = &model.Contact{Name: "base-contact", AccountID: s.account.ID}
+	s.db.Create(s.contact1)
+	s.contact2 = &model.Contact{Name: "target-contact", AccountID: s.account.ID}
+	s.db.Create(s.contact2)
+}
+
+func (s *ContactMergeHandlerTestSuite) TearDownSuite() {
+	if s.db != nil {
+		sqlDB, _ := s.db.DB()
+		sqlDB.Close()
+	}
+}
+
+func TestContactMergeHandlerSuite(t *testing.T) {
+	suite.Run(t, new(ContactMergeHandlerTestSuite))
+}
+
+func (s *ContactMergeHandlerTestSuite) TestCreate_Success() {
+	r := gin.New()
+	r.POST("/api/v1/accounts/:account_id/actions/contact_merge", func(c *gin.Context) {
+		c.Set("account_id", float64(s.account.ID))
+		c.Next()
+	}, s.handler.Create)
+
+	base := &model.Contact{Name: "merge-base", Email: "base@example.com", AccountID: s.account.ID}
+	mergee := &model.Contact{Name: "mergee-contact", PhoneNumber: "+12212345", AccountID: s.account.ID}
+	s.Require().NoError(s.db.Create(base).Error)
+	s.Require().NoError(s.db.Create(mergee).Error)
+
+	body := map[string]uint{"base_contact_id": base.ID, "mergee_contact_id": mergee.ID}
+	b, _ := json.Marshal(body)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", fmt.Sprintf("/api/v1/accounts/%d/actions/contact_merge", s.account.ID), bytes.NewBuffer(b))
+	req.Header.Set("Content-Type", "application/json")
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusOK, w.Code)
+	var payload map[string]any
+	s.Require().NoError(json.Unmarshal(w.Body.Bytes(), &payload))
+	assert.Equal(s.T(), float64(base.ID), payload["id"])
+	assert.Equal(s.T(), "base@example.com", payload["email"])
+	assert.NotContains(s.T(), payload, "success")
+	assert.NotContains(s.T(), payload, "data")
+}
+
+func (s *ContactMergeHandlerTestSuite) TestCreate_BadRequest_NoBody() {
+	r := gin.New()
+	r.POST("/api/v1/accounts/:account_id/actions/contact_merge", func(c *gin.Context) {
+		c.Set("account_id", float64(s.account.ID))
+		c.Next()
+	}, s.handler.Create)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", fmt.Sprintf("/api/v1/accounts/%d/actions/contact_merge", s.account.ID), nil)
+	req.Header.Set("Content-Type", "application/json")
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusBadRequest, w.Code)
+}
+
+func (s *ContactMergeHandlerTestSuite) TestCreate_BadRequest_InvalidAccountID() {
+	r := gin.New()
+	r.POST("/api/v1/accounts/:account_id/actions/contact_merge", s.handler.Create)
+
+	body := map[string]uint{"base_contact_id": s.contact1.ID, "mergee_contact_id": s.contact2.ID}
+	b, _ := json.Marshal(body)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", "/api/v1/accounts/abc/actions/contact_merge", bytes.NewBuffer(b))
+	req.Header.Set("Content-Type", "application/json")
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusBadRequest, w.Code)
+}