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/notion_integration_handler.go

@@ -0,0 +1,63 @@
+package v1
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/gochat/gochat/internal/service"
+	"github.com/gochat/gochat/pkg/response"
+)
+
+// NotionIntegrationHandler handles Notion integration endpoints.
+// Reference: Chatwoot Integrations::NotionController
+type NotionIntegrationHandler struct {
+	svc *service.NotionIntegrationService
+}
+
+// NewNotionIntegrationHandler creates a new NotionIntegrationHandler.
+func NewNotionIntegrationHandler(svc *service.NotionIntegrationService) *NotionIntegrationHandler {
+	return &NotionIntegrationHandler{svc: svc}
+}
+
+// Authorization creates a Notion OAuth authorization URL.
+// POST /api/v1/accounts/:account_id/notion/authorization
+func (h *NotionIntegrationHandler) Authorization(c *gin.Context) {
+	accountID, err := parseUintParam(c, "account_id")
+	if err != nil {
+		response.AbortWithStatusError(c, http.StatusBadRequest, response.ErrBadRequest, "invalid account_id")
+		return
+	}
+
+	result, svcErr := h.svc.BuildAuthorizationURL(accountID)
+	if svcErr != nil {
+		c.JSON(http.StatusUnprocessableEntity, gin.H{"success": false})
+		return
+	}
+	c.JSON(http.StatusOK, result)
+}
+
+// Delete removes a Notion integration for an account.
+// DELETE /api/v1/accounts/:account_id/integrations/notion
+func (h *NotionIntegrationHandler) Delete(c *gin.Context) {
+	accountID, err := parseUintParam(c, "account_id")
+	if err != nil {
+		response.AbortWithStatusError(c, http.StatusBadRequest, response.ErrBadRequest, "invalid account_id")
+		return
+	}
+
+	if svcErr := h.svc.Delete(c.Request.Context(), accountID); svcErr != nil {
+		handleServiceError(c, svcErr)
+		return
+	}
+	c.Status(http.StatusOK)
+}
+
+// RegisterNotionIntegrationRoutes registers Notion integration routes.
+func RegisterNotionIntegrationRoutes(g *gin.RouterGroup, h *NotionIntegrationHandler) {
+	g.DELETE("/notion", h.Delete)
+	notion := g.Group("/notion")
+	{
+		notion.DELETE("/", h.Delete)
+	}
+}