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/session/models.py

@@ -0,0 +1,64 @@
+from datetime import datetime
+from typing import Literal
+
+from pydantic import BaseModel, Field, ConfigDict
+
+
+# Stub locale di _YamlModel (in the reference implementation vive in mschema/models.py).
+# Qui serve solo come base con populate_by_name; mschema/ sara' portato nel Task A9.
+class _YamlModel(BaseModel):
+    model_config = ConfigDict(populate_by_name=True)
+
+
+class SessionManifest(_YamlModel):
+    id: str
+    created_at: datetime
+    status: Literal["open", "closed", "finalized"] = "open"
+    question: str
+    database: str
+    db_schema: str = Field(alias="schema")
+    # D12/D15: autore della sessione (auth) e versione del workflow usato.
+    author: str | None = None
+    summary: str | None = None
+    updated_at: datetime | None = None
+    updated_by: str | None = None
+    schema_version: int | None = None
+
+
+class Candidate(BaseModel):
+    kind: Literal["table", "column"]
+    name: str
+    signals: dict = {}
+    evidence: list[str] = []
+    decision: Literal["promoted", "excluded", "pending"] = "pending"
+    decision_seq: int | None = None
+    # D14a: valori citati nella domanda ancorati a questa colonna/tabella.
+    grounded_values: list[dict] = []
+
+
+class Join(BaseModel):
+    from_: str = Field(alias="from")
+    to: str
+    source: str = ""
+    decision: Literal["promoted", "excluded", "pending"] = "promoted"
+    decision_seq: int | None = None
+
+    model_config = {"populate_by_name": True}
+
+
+class ExcludedItem(BaseModel):
+    kind: Literal["table", "column"]
+    name: str
+    decision_seq: int | None = None
+
+
+class SchemaLinking(BaseModel):
+    question: str
+    candidates: list[Candidate] = []
+    joins: list[Join] = []
+    excluded: list[ExcludedItem] = []
+    open_questions: list[str] = []
+    # D14b: formule di concetto approvate, parte dello schema-linking.
+    concept_formulas: list[dict] = []
+
+    model_config = {"extra": "forbid"}