feat: implement metadata catalog database management

docs/architecture/components.md

@@ -4,7 +4,10 @@ This page complements the [architecture overview](overview.md) with the module s
 
 ## Modules and dependencies
 
-The frontend communicates with the backend through REST and SSE. The backend does not own session persistence: it starts Pi, invokes the `tht` CLI, and forwards events. The harness contains the workflow, the Python CLI, and adapters for the DWH and vector store.
+The frontend communicates with the backend through REST and SSE. The backend does not own session
+persistence: it starts Pi, invokes the `tht` CLI, and forwards events. It does own the separate
+installation-local database catalog. The harness contains the workflow, the Python CLI, and
+adapters for the DWH and vector store.
 
 ```mermaid
 flowchart LR
@@ -18,6 +21,8 @@ flowchart LR
     THT --> DWH["DWH\nread-only"]
     THT --> VDB["Qdrant / vector store"]
     BE --> CFG["settings.json\nworkspace registry"]
+    BE --> CAT["catalog-db\nPostgreSQL + Kysely"]
+    BE -->|catalog Test + Table Sync| DWH
     FE -.->|renders widgets| EXT
 ```
 
@@ -26,7 +31,7 @@ Dipendenze principali:
 | Module | Depends on | Responsibility |
 | --- | --- | --- |
 | `frontend/` | Backend REST and SSE APIs | UI, gate widgets, and in-memory transcript |
-| `backend/src/` | Pi, `tht`, configuration, and workspace registry | Transport, session lifecycle, and APIs |
+| `backend/src/` | Pi, `tht`, configuration, workspace registry, catalog PostgreSQL, and read-only DWH connectors | Transport, session lifecycle, catalog CRUD, connection tests, table introspection, and APIs |
 | `harness/.pi/` | Pi and `tht phase` | Workflow orchestration and human-in-the-loop gates |
 | `harness/tht/` | Filesystem, DWH, and vector store | Persistence, CLI, Evidence, schema, and preprocessing |
 | workspace repository | `source/`, `curated/`, manifest, and artifacts | Versioned Evidence source and session output |