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/agent_bot_inbox.go

@@ -0,0 +1,37 @@
+package model
+
+import (
+	"time"
+)
+
+// AgentBotInboxStatus represents the active/inactive state of a bot-inbox binding.
+type AgentBotInboxStatus int
+
+const (
+	AgentBotInboxActive   AgentBotInboxStatus = 0 // Bot is actively monitoring the inbox
+	AgentBotInboxInactive AgentBotInboxStatus = 1 // Bot binding paused (not deleted)
+)
+
+// AgentBotInbox represents the join between AgentBot and Inbox.
+// Reference: Chatwoot AgentBotInbox model + P2B M2/M12 spec
+// Supports active/inactive status control — allows pausing bot monitoring without deleting binding.
+// account_id is auto-populated from inbox.account_id (ensure_account_id callback).
+type AgentBotInbox struct {
+	ID        uint              `gorm:"primaryKey" json:"id"`
+	AgentBotID uint             `gorm:"not null;index" json:"agent_bot_id"`
+	InboxID   uint              `gorm:"not null;index" json:"inbox_id"`
+	AccountID *uint             `gorm:"index" json:"account_id,omitempty"` // inherited from Inbox
+	Status    AgentBotInboxStatus `gorm:"default:0" json:"status"` // 0=active, 1=inactive
+	CreatedAt time.Time         `gorm:"autoCreateTime" json:"created_at"`
+	UpdatedAt time.Time         `gorm:"autoUpdateTime" json:"updated_at"`
+
+	AgentBot AgentBot `gorm:"foreignKey:AgentBotID" json:"agent_bot,omitempty"`
+	Inbox    Inbox    `gorm:"foreignKey:InboxID" json:"inbox,omitempty"`
+}
+
+// IsActive returns true if the binding is in active state.
+func (abi *AgentBotInbox) IsActive() bool {
+	return abi.Status == AgentBotInboxActive
+}
+
+func (AgentBotInbox) TableName() string { return "agent_bot_inboxes" }