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/middleware/recovery.go

@@ -0,0 +1,29 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	applogger "github.com/gochat/gochat/pkg/logger"
+	"github.com/gochat/gochat/pkg/response"
+)
+
+// Recovery handles panic recovery and returns a 500 error.
+// Corresponds to Chatwoot's ActionDispatch::Reloader middleware.
+func Recovery() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		defer func() {
+			if err := recover(); err != nil {
+				applogger.L().Errorf("Panic recovered: %v\nPath: %s %s", err, c.Request.Method, c.Request.URL.Path)
+				c.AbortWithStatusJSON(http.StatusInternalServerError, response.APIResponse{
+					Success: false,
+					Error: &response.ErrorBody{
+						Code:    response.ErrInternal,
+						Message: "Internal server error",
+					},
+				})
+			}
+		}()
+		c.Next()
+	}
+}