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/model/conversation.go

@@ -0,0 +1,60 @@
+package model
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+
+	"gorm.io/datatypes"
+	"gorm.io/gorm"
+)
+
+// Conversation represents a conversation between a contact and agents.
+type Conversation struct {
+	Base
+	UUID                 string         `gorm:"type:uuid;uniqueIndex;not null" json:"uuid"` // auto-generated global unique identifier
+	DisplayID            *uint          `gorm:"index" json:"display_id,omitempty"`          // account-level auto-increment number
+	AccountID            uint           `gorm:"index;not null" json:"account_id"`
+	InboxID              uint           `gorm:"index;not null" json:"inbox_id"`
+	ContactID            uint           `gorm:"index;not null" json:"contact_id"`
+	ContactInboxID       *uint          `gorm:"index" json:"contact_inbox_id,omitempty"`
+	AssigneeID           *uint          `gorm:"index" json:"assignee_id"`
+	AssigneeAgentBotID   *uint          `gorm:"index" json:"assignee_agent_bot_id,omitempty"`
+	TeamID               *uint          `gorm:"index" json:"team_id,omitempty"`
+	CampaignID           *uint          `gorm:"index" json:"campaign_id,omitempty"`
+	SlaPolicyID          *uint          `gorm:"index" json:"sla_policy_id,omitempty"`
+	Status               string         `gorm:"size:50;index;default:open" json:"status"` // open, resolved, pending, snoozed
+	Priority             string         `gorm:"size:50;default:none" json:"priority"`     // none, low, medium, high, urgent
+	ChannelType          string         `gorm:"size:50;not null" json:"channel_type"`
+	Channel              string         `gorm:"size:50;not null" json:"channel"`      // channel identifier for routing
+	Labels               string         `gorm:"type:text" json:"labels,omitempty"`    // comma-separated or JSON label list
+	SnoozedUntil         *int64         `gorm:"index" json:"snoozed_until,omitempty"` // timestamp for snoozed conversations
+	AdditionalAttributes datatypes.JSON `gorm:"type:jsonb" json:"additional_attributes,omitempty"`
+	CustomAttributes     datatypes.JSON `gorm:"type:jsonb" json:"custom_attributes,omitempty"`
+	AgentLastSeenAt      *int64         `json:"agent_last_seen_at,omitempty"`
+	AssigneeLastSeenAt   *int64         `json:"assignee_last_seen_at,omitempty"`
+	ContactLastSeenAt    *int64         `json:"contact_last_seen_at,omitempty"`
+	WaitingSince         *int64         `json:"waiting_since,omitempty"`
+	LastActivityAt       *int64         `json:"last_activity_at,omitempty"`
+	FirstReplyCreatedAt  *int64         `json:"first_reply_created_at,omitempty"`
+	Muted                bool           `gorm:"default:false" json:"muted"`
+	ResolvedAt           *time.Time     `json:"resolved_at,omitempty"` // Chatwoot: timestamp when conversation was resolved
+	ResumedAt            *time.Time     `json:"resumed_at,omitempty"`  // Chatwoot: timestamp when conversation was reopened
+	LastMessageAt        *int64         `gorm:"index" json:"last_message_at,omitempty"`
+	LastNonSysMsgAt      *int64         `json:"last_non_system_message_at,omitempty"`
+
+	Contact  *Contact  `gorm:"foreignKey:ContactID" json:"contact,omitempty"`
+	Inbox    *Inbox    `gorm:"foreignKey:InboxID" json:"inbox,omitempty"`
+	Assignee *User     `gorm:"foreignKey:AssigneeID" json:"assignee,omitempty"`
+	Messages []Message `gorm:"foreignKey:ConversationID" json:"messages,omitempty"`
+}
+
+// BeforeCreate auto-generates UUID before inserting a new Conversation record.
+func (c *Conversation) BeforeCreate(tx *gorm.DB) error {
+	if c.UUID == "" {
+		c.UUID = uuid.New().String()
+	}
+	return nil
+}
+
+func (Conversation) TableName() string { return "conversations" }