refactor(harness): renaming prodotto tht (Onda -1)

Thoth (tht) è il prodotto, PSD è il cliente. Nessun riferimento al contesto
clinico nel codice.

Rinomine:
- comando+package nsp→tht (dir nsp/→tht/, 46 import, pyproject entry point)
- gate nsp-gate.js→tht-gate.js (+ rewrite token, relayIfNspFails→relayIfThtFails)
- workspace chirone.{example,test}.yaml→tht.{example,test}.yaml (generici)
- env THOTH_→THT_ (19 var) + NSP_ stragglers (NSP_HARNESS_ROOT, NSP_SESSION)
- commenti/docstring chirone/psdwp3/policlinico neutralizzati ('the reference
  implementation', 'the DWH')

Aggiunto [tool.setuptools.packages.find] include=['tht*'] (necessario: l'auto-
discovery rompeva con tht/ + workspaces/ come top-level multipli).

.env operatore aggiornato in-place (prefissi THT_, valori preservati, gitignored).

Verifica: pytest 109 passed, npm test 14 pass, tht phase meta --json OK, zero
residui nsp/THOTH_/NSP_/chirone nel package.

harness/tht/db/connection.py

@@ -0,0 +1,37 @@
+from sqlalchemy import Engine, create_engine, text
+
+from tht.config import DatabaseConfig
+
+
+def make_engine(cfg: DatabaseConfig) -> Engine:
+    url = (
+        f"postgresql+psycopg2://{cfg.user}:{cfg.password}"
+        f"@{cfg.host}:{cfg.port}/{cfg.database}"
+    )
+    return create_engine(url, echo=False)
+
+
+def ping(engine: Engine) -> None:
+    with engine.connect() as conn:
+        conn.execute(text("SELECT 1"))
+
+
+def writable_tables(engine: Engine, schema: str) -> list[str]:
+    """Tabelle dello schema su cui l'utente corrente ha privilegi di scrittura."""
+    q = text("""
+        SELECT c.relname
+        FROM pg_class c
+        JOIN pg_namespace n ON n.oid = c.relnamespace
+        WHERE n.nspname = :schema
+          AND c.relkind IN ('r', 'p')
+          AND has_table_privilege(current_user, c.oid, 'INSERT, UPDATE, DELETE')
+        ORDER BY c.relname
+    """)
+    with engine.connect() as conn:
+        return [row[0] for row in conn.execute(q, {"schema": schema})]
+
+
+def can_create_in_schema(engine: Engine, schema: str) -> bool:
+    q = text("SELECT has_schema_privilege(current_user, :schema, 'CREATE')")
+    with engine.connect() as conn:
+        return bool(conn.execute(q, {"schema": schema}).scalar())