feat(amendment): ROUND 2 — scheduler + upload documenti

Seconda parte della replica soccorso istruttorio speculare al BE Gepafin.
Completata: scheduler cron (expire + reminder), upload documenti istruttore
e benef, fix duplicati config.

==SCHEDULER (app/scheduler.py NUOVO)==
APScheduler BackgroundScheduler integrato nel lifespan FastAPI.
Due cron attivi (timezone Europe/Rome):

  expire_amendments() - cron 01:05 ogni notte
    Speculare a ApplicationAmendmentScheduler.processAmendmentExpirationScheduler.
    Trova amendment AWAITING con deadline < today, passa a EXPIRED.
    Rimette pratica a UNDER_REVIEW se non ha altri amendment aperti.
    Ritorna dict stats per logging/test.

  queue_reminders() - cron 09:00 ogni mattina
    Speculare a ExpirationScheduler.processAmendmentExpiration (data-driven).
    Legge remission_expiration_config (type='AMENDMENT', interval_days=N),
    per ogni riga trova amendment con deadline esattamente today+N e setta
    pec_retry_after (marker che il BE vede via /internal pending-reminder).
    Multipli row = multipli reminder (seed: 7gg + 2gg).

Il microservizio aggiorna solo stato DB. L invio effettivo di email
reminder lo fa il BE Gepafin tramite polling, tenant-aware.

==UPLOAD DOCUMENTI==
3 nuovi endpoint nel router istruttoria:

  POST   /instructor/{pid}/amendment/{aid}/upload-document
    - Istruttore allega PDF al soccorso (motivazione, scheda tecnica).
    - Consentito in DRAFT o AWAITING. Sostituisce precedente se esiste.
    - Popola amendment_document_path + amendment_document_type.

  DELETE /instructor/{pid}/amendment/{aid}/upload-document
    - Rimuove allegato (solo in DRAFT).

  POST   /instructor/{pid}/amendment/{aid}/upload-response-document
    - Benef allega PDF come supporto alla risposta.
    - Consentito in AWAITING/RESPONSE_RECEIVED, solo proprietario.
    - Popola response_document_path + response_document_type.

Riusa save_upload() esistente con entity_type dedicati.

==FIX storage.py==
Whitelist entity_type estesa con 'amendment-instructor-doc' +
'amendment-response-doc' (prima accettava solo invoice/ula/document,
bloccando l'upload con StorageError).

==FIX migration dedup==
Scoperto in test: migration 8 faceva INSERT ON CONFLICT DO NOTHING su
remission_expiration_config ma senza UNIQUE constraint. Ogni restart
inseriva duplicati (16 righe in DB invece di 2). Fix in migration 9:
DELETE duplicati + ADD UNIQUE (type, interval_days) + re-seed pulito.

==REQUIREMENTS==
APScheduler==3.10.4

==TEST E2E==
/tmp/test_amendment_r2_fixed.py passa su tutto:
  [A] upload amendment_document istruttore + response_document benef + respond
  [B] amendment scaduto artificiale -> expire_amendments lo marca EXPIRED,
      pratica torna UNDER_REVIEW
  [C] amendment a +2gg e +7gg -> queue_reminders accoda 2 reminder,
      /internal pending-reminder li espone entrambi

app/migrations.py

@@ -155,9 +155,29 @@ MIGRATIONS = [
     CREATE INDEX IF NOT EXISTS idx_expiration_config_type
         ON gepafin_rendic.remission_expiration_config(type)
         WHERE is_deleted = false;
+    """,
+    # 2026-04-20 v5: dedup duplicati (ON CONFLICT DO NOTHING non funzionava senza UNIQUE)
+    # + aggiungo UNIQUE constraint per prevenire futuri duplicati
+    """
+    DELETE FROM gepafin_rendic.remission_expiration_config ec
+    USING gepafin_rendic.remission_expiration_config ec2
+    WHERE ec.id > ec2.id
+      AND ec.type = ec2.type
+      AND ec.interval_days = ec2.interval_days;
+    DO $$
+    BEGIN
+        IF NOT EXISTS (
+            SELECT 1 FROM pg_constraint
+            WHERE conname = 'uq_expiration_config_type_days'
+              AND conrelid = 'gepafin_rendic.remission_expiration_config'::regclass
+        ) THEN
+            ALTER TABLE gepafin_rendic.remission_expiration_config
+                ADD CONSTRAINT uq_expiration_config_type_days UNIQUE (type, interval_days);
+        END IF;
+    END$$;
     INSERT INTO gepafin_rendic.remission_expiration_config (type, interval_days)
     VALUES ('AMENDMENT', 7), ('AMENDMENT', 2)
-    ON CONFLICT DO NOTHING;
+    ON CONFLICT (type, interval_days) DO NOTHING;
     """,
 ]