feat(harness): port backend Onda 0 — vendor, lshindex, sqlcheck, execute, rest/exec, ctetest, report, datamart

8 moduli leaf portati verbatim da ChironeWp3 con rename psdwp3→tht:
- vendor/thoth_lsh (MinHash/LSH, leaf puro datasketch+tqdm) + VENDORED.md
- lshindex/ (build/save/load/query, dipende vendor + LshConfig)
- sqlcheck/ (validate_sql, leaf ExecutionConfig+mschema)
- execute/ + execute/warnings (run_controlled/explain, leaf sqlglot+sqlalchemy)
- rest/execute + rest/explain (REST variants, dipendono execute+rest.client)
- ctetest (CTE test records, leaf sqlglot+pydantic)
- report (validation report rendering, dipende execute+sqlcheck)
- datamart (stub NotImplementedError)

Verifica: import smoke catena completa OK, pytest 109 passed. Deps (datasketch, sqlglot,
sqlalchemy, pydantic, requests, tqdm) già in pyproject. VENDORED.md neutralizzato
(riferimenti PsdWp3→Thoth).

harness/tht/rest/explain.py

@@ -0,0 +1,35 @@
+"""Parsing del piano EXPLAIN testuale restituito dall'rpc `explain_query`.
+
+Il transport diretto usa `EXPLAIN (FORMAT JSON)`; via REST l'rpc ritorna il piano come
+righe di testo (formato default di EXPLAIN). Questo modulo le riconduce a `PlanSummary`,
+così la logica a valle (`plan_warnings`, display) non cambia.
+"""
+
+import re
+
+from tht.execute import ExecutionError, PlanSummary
+
+# es. "(cost=0.00..3712.97 rows=13706 width=0)"
+_COST_RE = re.compile(r"\(cost=[\d.]+\.\.([\d.]+)\s+rows=(\d+)\s+width=\d+\)")
+
+
+def parse_text_plan(lines: list[str]) -> PlanSummary:
+    node_types: list[str] = []
+    total_cost = 0.0
+    plan_rows = 0
+    root_seen = False
+    for line in lines:
+        m = _COST_RE.search(line)
+        if m is None:
+            # riga di dettaglio (Filter, Index Cond, …): non è un nodo del piano
+            continue
+        label = line.split("(cost=")[0].replace("->", " ").strip()
+        if label:
+            node_types.append(label)
+        if not root_seen:
+            total_cost = float(m.group(1))
+            plan_rows = int(m.group(2))
+            root_seen = True
+    if not root_seen:
+        raise ExecutionError("piano EXPLAIN vuoto o non interpretabile")
+    return PlanSummary(total_cost=total_cost, plan_rows=plan_rows, node_types=node_types)