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/csat/model.go

@@ -0,0 +1,26 @@
+package csat
+
+import (
+	"time"
+
+	"github.com/gochat/gochat/internal/model"
+)
+
+// CsatSurveyResponse stores a customer satisfaction survey response.
+// Reference: Chatwoot CSAT survey response model — captures rating (1-5), feedback_message,
+// review_notes, and links to conversation/message/agent.
+type CsatSurveyResponse struct {
+	model.Base
+	AccountID         uint      `gorm:"index;not null" json:"account_id"`
+	ConversationID    uint      `gorm:"index;not null" json:"conversation_id"`
+	ContactID         uint      `gorm:"index;not null" json:"contact_id"`
+	MessageID         uint      `gorm:"index;not null" json:"message_id"`
+	AssignedAgentID   *uint     `gorm:"index" json:"assigned_agent_id,omitempty"`
+	Rating            int       `gorm:"not null;check:rating >= 1 AND rating <= 5" json:"rating"` // 1-5
+	FeedbackMessage   string    `gorm:"type:text" json:"feedback_message"`
+	CsatReviewNotes   string    `gorm:"type:text" json:"csat_review_notes"`
+	ReviewNotesUpdatedAt *time.Time `json:"review_notes_updated_at,omitempty"`
+	ReviewNotesUpdatedByID *uint `json:"review_notes_updated_by_id,omitempty"`
+}
+
+func (CsatSurveyResponse) TableName() string { return "csat_survey_responses" }