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/reporting/model.go

@@ -0,0 +1,32 @@
+package reporting
+
+// Model types are defined in the model package to avoid duplication and ensure
+// a single source of truth for GORM migrations and cross-package references.
+// This file only re-exports them for convenience within the reporting package.
+
+import (
+	"github.com/gochat/gochat/internal/model"
+)
+
+// Re-export model types for convenient use within the reporting package.
+type ReportingEvent = model.ReportingEvent
+type ReportingEventsRollup = model.ReportingEventsRollup
+type DimensionType = model.DimensionType
+type RollupMetric = model.RollupMetric
+
+// Re-export constants.
+const (
+	DimensionAccount = model.DimensionAccount
+	DimensionAgent   = model.DimensionAgent
+	DimensionInbox   = model.DimensionInbox
+	DimensionTeam    = model.DimensionTeam
+)
+
+const (
+	MetricResolutionsCount    = model.MetricResolutionsCount
+	MetricFirstResponse       = model.MetricFirstResponse
+	MetricResolutionTime      = model.MetricResolutionTime
+	MetricReplyTime           = model.MetricReplyTime
+	MetricBotResolutionsCount = model.MetricBotResolutionsCount
+	MetricBotHandoffsCount    = model.MetricBotHandoffsCount
+)