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/banner_handler_test.go

@@ -0,0 +1,150 @@
+package v1
+
+import (
+	"bytes"
+	"encoding/json"
+	"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 BannerHandlerTestSuite struct {
+	suite.Suite
+	db      *gorm.DB
+	handler *BannerHandler
+}
+
+func (s *BannerHandlerTestSuite) 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.Banner{}))
+	s.db = db
+
+	repo := repository.NewBannerRepo(db)
+	svc := service.NewBannerService(repo)
+	s.handler = NewBannerHandler(svc)
+}
+
+func (s *BannerHandlerTestSuite) TearDownSuite() {
+	if s.db != nil {
+		sqlDB, _ := s.db.DB()
+		sqlDB.Close()
+	}
+}
+
+func TestBannerHandlerSuite(t *testing.T) {
+	suite.Run(t, new(BannerHandlerTestSuite))
+}
+
+func (s *BannerHandlerTestSuite) TestList_Success() {
+	r := gin.New()
+	r.GET("/platform/api/v1/banners", s.handler.List)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/platform/api/v1/banners", nil)
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusOK, w.Code)
+}
+
+func (s *BannerHandlerTestSuite) TestListActive_Success() {
+	r := gin.New()
+	r.GET("/platform/api/v1/banners/active", s.handler.ListActive)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/platform/api/v1/banners/active", nil)
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusOK, w.Code)
+}
+
+func (s *BannerHandlerTestSuite) TestCreate_BadRequest_EmptyBody() {
+	r := gin.New()
+	r.POST("/platform/api/v1/banners", s.handler.Create)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", "/platform/api/v1/banners", nil)
+	req.Header.Set("Content-Type", "application/json")
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusBadRequest, w.Code)
+}
+
+func (s *BannerHandlerTestSuite) TestCreate_Success() {
+	r := gin.New()
+	r.POST("/platform/api/v1/banners", s.handler.Create)
+
+	body := map[string]interface{}{
+		"title":       "System Update",
+		"content":     "New features available",
+		"active":      true,
+		"banner_type": "update",
+		"created_by":  1,
+	}
+	b, _ := json.Marshal(body)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", "/platform/api/v1/banners", bytes.NewBuffer(b))
+	req.Header.Set("Content-Type", "application/json")
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusCreated, w.Code)
+}
+
+func (s *BannerHandlerTestSuite) TestGet_BadRequest_InvalidID() {
+	r := gin.New()
+	r.GET("/platform/api/v1/banners/:id", s.handler.Get)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/platform/api/v1/banners/abc", nil)
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusBadRequest, w.Code)
+}
+
+func (s *BannerHandlerTestSuite) TestGet_NotFound() {
+	r := gin.New()
+	r.GET("/platform/api/v1/banners/:id", s.handler.Get)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/platform/api/v1/banners/99999", nil)
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusNotFound, w.Code)
+}
+
+func (s *BannerHandlerTestSuite) TestUpdate_BadRequest_InvalidID() {
+	r := gin.New()
+	r.PUT("/platform/api/v1/banners/:id", s.handler.Update)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("PUT", "/platform/api/v1/banners/abc", nil)
+	req.Header.Set("Content-Type", "application/json")
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusBadRequest, w.Code)
+}
+
+func (s *BannerHandlerTestSuite) TestDelete_BadRequest_InvalidID() {
+	r := gin.New()
+	r.DELETE("/platform/api/v1/banners/:id", s.handler.Delete)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("DELETE", "/platform/api/v1/banners/abc", nil)
+	r.ServeHTTP(w, req)
+
+	assert.Equal(s.T(), http.StatusBadRequest, w.Code)
+}