feat: implement metadata catalog database management

docs/guida-utente.md

@@ -92,8 +92,10 @@ evidence:
 
 Changes from older workspaces:
 
-- the database is reached only through **REST** or **direct Postgres** (`rest_api` /
-  `postgres_direct`); the SSH tunnel remains disabled;
+- NL→SQL sessions reach the database only through **REST** or **direct Postgres** (`rest_api` /
+  `postgres_direct`); `ssh_tunnel` remains disabled for session runtime. The separate Database
+  management surface supports SSH for **Test connection** and **Sync tables**, with a private key,
+  mandatory `known_hosts`, and an optional key passphrase;
 - the semantic index is **internal** (Qdrant plus `qwen3-embedding:0.6b`, 1024 dimensions, cosine);
 - **filesystem** Evidence lives in the repository (`<id>/evidence`) and is materialized from the
   pinned Git commit (P6). HTTP Evidence is also supported.