chore(legacy): relocate v1 dataconnect source

legacy/dataconnect-v1/README.md

@@ -0,0 +1,23 @@
+# Legacy Data Connect V1
+
+This directory contains the archived V1 Firebase Data Connect source:
+
+- GraphQL schemas
+- connector queries and mutations
+- seed and clean scripts
+- Data Connect service YAML files
+
+Status:
+
+- Treat this directory as legacy infrastructure.
+- Do not use it as the source of truth for new backend work.
+- The active backend architecture is V2 and lives under:
+  - `backend/command-api`
+  - `backend/query-api`
+  - `backend/core-api`
+  - `backend/unified-api`
+
+Why this was moved:
+
+- The old V1 GraphQL source was being picked up by AI tooling and confusing current V2 implementation work.
+- Relocating it under `legacy/` keeps the V1 toolchain available without presenting it as the active backend.