fix(harness): workspace + write-URL + L2 tests per accesso REST reale

Bug trovato provando la connessione reale col .env: il write endpoint vive su un
PATH DEDICATO /vector/write/v1/ (non /vector/v1/), e il modello Config ha write_rest/
vector_write_rest a TOP-LEVEL (non nidificati in vector_db).

- .env.example: aggiunge THOTH_VEC_WRITE_REST_URL (path dedicato del writer, con
  avviso che le due chiavi valgono su path separati).
- workspaces/chirone-test.yaml: riscritto allineato a chirone.example.yaml + config.py
  (vector_rest/vector_write_rest top-level; write_rest punta a THOTH_VEC_WRITE_REST_URL).
- tests/l2/*: corretti gli accessi strutturali (ws.vector_write_rest invece di
  ws.vector_db.write_rest; ws.vector_rest invece di ws.vector_db.rest).
  test_value_grounding_real skip-when-import-fails su nsp.lshindex (modulo deferred da B3).

Verificato end-to-end: save_one_memory (embeddings -> writer REST /vector/write/v1/
-> upsert pgvector -> read-back reader) PASSED. Suite L0+L1: 109 passed. Suite L2:
4 passed, 1 skipped (lshindex deferred).

Nota operativa: THOTH_SSL_CA va lasciato VUOTO sulla workstation (cert GoDaddy
pubblico in certifi). I campi direct-transport (THOTH_DB_*, THOTH_VEC_PASSWORD)
sono obbligatori per il modello ma inutilizzati in transport=rest: riempiti con
dummy nel .env locale (come faceva ChironeWp3).

harness/tests/l2/test_value_grounding_real.py

@@ -21,7 +21,10 @@ def test_ablazione_returns_multiple_columns(l2_env):
     a flag and a free-text patologia field) -- the whole point of D14a's
     non-collapsing aggregation. Requires a built LSH index (nsp lsh build)."""
     from nsp.config import LshConfig
-    from nsp.lshindex import load_index, query_index  # ported with the lsh build path
+    try:
+        from nsp.lshindex import load_index, query_index  # ported with the lsh build path
+    except ModuleNotFoundError:
+        pytest.skip("nsp.lshindex not yet ported (deferred from B3; lands with nsp lsh build)")
     from nsp.search import aggregate_lsh_multi
 
     # NOTE: this test assumes the LSH index was built (nsp lsh build --workspace