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/data_source.go

@@ -0,0 +1,64 @@
+package reporting
+
+import (
+	"time"
+)
+
+// TimeseriesPoint represents a single data point in a timeseries.
+type TimeseriesPoint struct {
+	Timestamp time.Time `json:"timestamp"`
+	Value     float64   `json:"value"`
+}
+
+// AggregateResult holds a single aggregate value for a metric.
+type AggregateResult struct {
+	Metric string  `json:"metric"`
+	Value  float64 `json:"value"`
+}
+
+// SummaryResult holds the summary (totals/averages) for a metric over a range.
+type SummaryResult struct {
+	Metric    string  `json:"metric"`
+	Total     float64 `json:"total"`
+	Average   float64 `json:"average"`
+	Count     int     `json:"count"`
+}
+
+// DataSourceParams defines the parameters for a data source query.
+// Reference: Chatwoot Reports::DataSource — for(account, metric, dimension_type, dimension_id,
+// range, group_by, timezone_offset, business_hours)
+type DataSourceParams struct {
+	AccountID         uint
+	Metric            string
+	DimensionType     DimensionType
+	DimensionID       uint
+	Since             time.Time
+	Until             time.Time
+	GroupBy           string // day, week, month
+	TimezoneOffset    int    // hours offset from UTC
+	BusinessHours     bool
+}
+
+// DataSource is the interface for fetching report data (timeseries, aggregate, summary).
+// Reference: Chatwoot Reports::DataSource base class.
+type DataSource interface {
+	// Timeseries returns a time-bucketed series of data points.
+	Timeseries(params DataSourceParams) ([]TimeseriesPoint, error)
+	// Aggregate returns a single aggregate value for the metric.
+	Aggregate(params DataSourceParams) (*AggregateResult, error)
+	// Summary returns total, average, and count for the metric over the range.
+	Summary(params DataSourceParams) (*SummaryResult, error)
+}
+
+// RawDataSource queries raw reporting_events for timeseries/aggregate/summary.
+// Reference: Chatwoot Reports::RawDataSource
+type RawDataSource struct{}
+
+// NewRawDataSource creates a new raw data source.
+func NewRawDataSource() *RawDataSource {
+	return &RawDataSource{}
+}
+
+// Note: Timeseries, Aggregate, Summary implementations on RawDataSource will be
+// wired through ReportingService which holds the DB connection.
+// The DataSource interface allows swapping between RawDataSource and RollupDataSource.