feat(stats): add vehicle data source metadata

.superpowers/sdd/task-1-report.md

@@ -0,0 +1,54 @@
+# Task 1 Report: Source Metadata Schema And Identity Helpers
+
+## Outcome
+- Implemented Task 1 in `go/vehicle-gateway/internal/stats`.
+- Added source metadata schema, identity helpers, and focused tests.
+
+## RED Evidence
+Initial focused test run failed as expected because the new helpers did not exist yet:
+
+```bash
+cd /Users/lingniu/project/ai-coding/lingniu-vehicle-ingest/go/vehicle-gateway
+go test ./internal/stats -run 'TestNormalizeSourceIP|TestNewSourceIdentity|TestUpsertDataSource' -count=1
+```
+
+Result:
+- `undefined: NormalizeSourceIP`
+- `undefined: NewSourceIdentity`
+- `undefined: SourceIdentity`
+- `undefined: UpsertDataSource`
+
+## GREEN Evidence
+After implementation, the focused tests passed:
+
+```bash
+cd /Users/lingniu/project/ai-coding/lingniu-vehicle-ingest/go/vehicle-gateway
+go test ./internal/stats -run 'TestNormalizeSourceIP|TestNewSourceIdentity|TestUpsertDataSource' -count=1
+```
+
+Result:
+- `ok  	lingniu-vehicle-ingest/go/vehicle-gateway/internal/stats	0.927s`
+
+Full package verification also passed:
+
+```bash
+cd /Users/lingniu/project/ai-coding/lingniu-vehicle-ingest/go/vehicle-gateway
+go test ./internal/stats -count=1
+```
+
+Result:
+- `ok  	lingniu-vehicle-ingest/go/vehicle-gateway/internal/stats	0.355s`
+
+## Files Changed
+- `go/vehicle-gateway/internal/stats/schema.go`
+- `go/vehicle-gateway/internal/stats/source.go`
+- `go/vehicle-gateway/internal/stats/source_test.go`
+
+## Notes
+- `DataSourceTableSQL` was added verbatim to `schema.go` for the future schema wiring step.
+- `UpsertDataSource` follows the brief exactly, including the nil exec panic, empty-source short circuit, and SQL shape.
+
+## Self-Review
+- The implementation is tightly scoped to Task 1.
+- The new tests cover IP normalization, identity construction, and the SQL shape for the upsert helper.
+- No additional concerns at this stage.