feat: endpoint istruttore (queue + review + soccorso istruttorio)

- 4 nuove colonne su remission_practice: assigned_instructor_id, reviewed_at,
  reviewed_by, rejection_reason, approved_remission
- Nuova tabella remission_amendment_request con cascade delete, scope JSONB,
  stati AWAITING -> RESPONSE_RECEIVED -> CLOSED / EXPIRED / REJECTED
- Router instructor.py (287 righe) con 8 endpoint:
  /queue, /{id}, /{id}/claim, /{id}/approve, /{id}/reject,
  /{id}/amendment, /{id}/amendment/{aid}/close,
  /{id}/amendment/{aid}/respond-beneficiary
- GET /{id} (router practices) ora include amendments nel payload
- Manager manager_view flag per ROLE_INSTRUCTOR_MANAGER + SUPER_ADMIN
  (vede tutto il pool vs solo le proprie assegnazioni)
- Logica status transitions verificata:
  SUBMITTED -> UNDER_REVIEW (claim)
  UNDER_REVIEW <-> AWAITING_AMENDMENT (amendment open/close)
  UNDER_REVIEW | AWAITING_AMENDMENT -> APPROVED | REJECTED
- _compute_gate_check riusato anche dal router istruttore per calcolo
  remission_due in coda e nel dettaglio

Test end-to-end verde: ciclo completo benef -> istruttore -> soccorso ->
risposta -> chiusura -> approvazione funzionante su NAPOLI SAS.

app/models.py

@@ -61,6 +61,13 @@ class RemissionPractice(Base):
     amount_erogato = Column(Numeric(14, 2), nullable=False)  # copiato da application.amount_accepted
     notes_beneficiario = Column(Text, nullable=True)
 
+    # colonne istruttoria
+    assigned_instructor_id = Column(Integer, nullable=True)
+    reviewed_at = Column(DateTime(timezone=True), nullable=True)
+    reviewed_by = Column(Integer, nullable=True)
+    rejection_reason = Column(Text, nullable=True)
+    approved_remission = Column(Numeric(14, 2), nullable=True)
+
     created_at = Column(DateTime(timezone=True), nullable=False, server_default=func.now())
     updated_at = Column(DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now())
     submitted_at = Column(DateTime(timezone=True), nullable=True)
@@ -69,6 +76,7 @@ class RemissionPractice(Base):
     invoices = relationship("RemissionInvoice", back_populates="practice", cascade="all, delete-orphan")
     ula_employees = relationship("RemissionUlaEmployee", back_populates="practice", cascade="all, delete-orphan")
     documents = relationship("RemissionDocument", back_populates="practice", cascade="all, delete-orphan")
+    amendment_requests = relationship("RemissionAmendmentRequest", back_populates="practice", cascade="all, delete-orphan")
 
 
 class RemissionInvoice(Base):
@@ -141,3 +149,30 @@ class RemissionDocument(Base):
     notes = Column(Text, nullable=True)
 
     practice = relationship("RemissionPractice", back_populates="documents")
+
+
+class RemissionAmendmentRequest(Base):
+    """Richiesta di soccorso istruttorio: istruttore chiede integrazioni al beneficiario."""
+    __tablename__ = "remission_amendment_request"
+    __table_args__ = ({"schema": "gepafin_rendic"},)
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    practice_id = Column(UUID(as_uuid=True),
+                         ForeignKey("gepafin_rendic.remission_practice.id", ondelete="CASCADE"),
+                         nullable=False)
+    requested_by = Column(Integer, nullable=False)
+    request_text = Column(Text, nullable=False)
+    scope = Column(JSONB, nullable=True, default=dict)
+    deadline = Column(Date, nullable=False)
+    status = Column(String(32), nullable=False, default="AWAITING")
+    # AWAITING -> RESPONSE_RECEIVED -> CLOSED | EXPIRED | REJECTED
+
+    response_text = Column(Text, nullable=True)
+    response_at = Column(DateTime(timezone=True), nullable=True)
+    closed_at = Column(DateTime(timezone=True), nullable=True)
+    closed_by = Column(Integer, nullable=True)
+
+    created_at = Column(DateTime(timezone=True), nullable=False, server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now())
+
+    practice = relationship("RemissionPractice", back_populates="amendment_requests")