feat(v2): multi-tranche DB schema + gate cumulativo 5 voci Cecilia

A1 migrations.py:
- remission_practice DROP uq_application + ADD sequence_number/period_label/suggested_instructor_id
- UNIQUE composita (application_id, sequence_number)
- partial index idx_remission_practice_unassigned su assigned_instructor_id NULL
- nuova tabella remission_custom_check_value (storage_path/mime/size/sha256 allineata adapter)

A2 models.py + templates.py:
- RemissionPractice: UniqueConstraint composita, campi multi-tranche, relationship custom_checks
- classe RemissionCustomCheckValue
- RESTART_TEMPLATE schema_version=2, max_tranches=2, custom_checks esempio
  (antiriciclaggio required no-doc, polizza_fidejussoria optional con-doc)
- upgrade_schema_to_v2 idempotente per snapshot v1 esistenti

A3 _compute_gate_check(db, practice) CUMULATIVO:
- max_remission_global = min(cap_pct * erogato, cap_abs)
- already_approved = func.sum(approved_remission) su tranche APPROVED precedenti
  dello stesso application_id con sequence_number < corrente
- max_remission_this_tranche = max(0, global - already_approved)
- pre_check_admissible = min(grand_total_declared, this_tranche)  [voce 2 Cecilia]
- remission_due = min(effective_total, this_tranche)
- residuo_da_restituire = erogato - already_approved - remission_due (cumulativo)
- output totals esteso: sequence_number, tranches_count, tranches_max
- signature (db, practice) - aggiornati 6 call site in practices/instructor/verbale

Test su NAPOLI SAS: erogato 17K, cap 8500, tranche 1 approvata 467.14EUR,
tranche 2 vuota -> residuo disponibile 8032.86EUR, residuo_da_restituire 16532.86EUR.

app/migrations.py

@@ -41,6 +41,60 @@ MIGRATIONS = [
         ADD COLUMN IF NOT EXISTS sha256 varchar(64),
         ADD COLUMN IF NOT EXISTS uploaded_by integer;
     """,
+    # 2026-04-18 v2: multi-tranche su remission_practice
+    # DROP UNIQUE su application_id (permette piu tranche per stessa domanda)
+    # aggiunge sequence_number, period_label, suggested_instructor_id
+    # nuova UNIQUE (application_id, sequence_number)
+    # partial index su assigned_instructor_id IS NULL per coda "da assegnare"
+    """
+    ALTER TABLE gepafin_rendic.remission_practice
+        DROP CONSTRAINT IF EXISTS uq_remission_practice_application;
+    ALTER TABLE gepafin_rendic.remission_practice
+        ADD COLUMN IF NOT EXISTS sequence_number integer NOT NULL DEFAULT 1,
+        ADD COLUMN IF NOT EXISTS period_label varchar(100),
+        ADD COLUMN IF NOT EXISTS suggested_instructor_id integer;
+    DO $$
+    BEGIN
+        IF NOT EXISTS (
+            SELECT 1 FROM pg_constraint
+            WHERE conname = 'uq_remission_practice_app_seq'
+              AND conrelid = 'gepafin_rendic.remission_practice'::regclass
+        ) THEN
+            ALTER TABLE gepafin_rendic.remission_practice
+                ADD CONSTRAINT uq_remission_practice_app_seq UNIQUE (application_id, sequence_number);
+        END IF;
+    END$$;
+    CREATE INDEX IF NOT EXISTS idx_remission_practice_unassigned
+        ON gepafin_rendic.remission_practice(assigned_instructor_id)
+        WHERE assigned_instructor_id IS NULL;
+    """,
+    # 2026-04-18 v2: tabella custom checks
+    # allineata allo storage adapter esistente (storage_path + mime + size + sha256)
+    # NON segue le specs RAG p1 che usavano document_filename (v1 obsoleta)
+    """
+    CREATE TABLE IF NOT EXISTS gepafin_rendic.remission_custom_check_value (
+        id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+        practice_id uuid NOT NULL REFERENCES gepafin_rendic.remission_practice(id) ON DELETE CASCADE,
+        check_code varchar(64) NOT NULL,
+        beneficiary_declared boolean NOT NULL DEFAULT false,
+        declared_at timestamptz,
+        storage_path varchar(1024),
+        mime varchar(128),
+        size_bytes bigint,
+        sha256 varchar(64),
+        document_uploaded_at timestamptz,
+        uploaded_by integer,
+        verification_status varchar(20) NOT NULL DEFAULT 'PENDING',
+        verification_notes text,
+        verified_by integer,
+        verified_at timestamptz,
+        created_at timestamptz NOT NULL DEFAULT NOW(),
+        updated_at timestamptz NOT NULL DEFAULT NOW(),
+        CONSTRAINT uq_custom_check_practice_code UNIQUE (practice_id, check_code)
+    );
+    CREATE INDEX IF NOT EXISTS idx_custom_check_practice
+        ON gepafin_rendic.remission_custom_check_value(practice_id);
+    """,
 ]