feat(db): migrate to PostgreSQL 16 standalone

- docker-compose.prod.yml: add postgres:16-alpine service with health check,
  dedicated prod_leopost_net, backup volume mount, connection pool
- requirements.txt: add psycopg2-binary==2.9.9
- database.py: remove SQLite-specific run_migrations(), add PG pool_size/
  max_overflow/pool_pre_ping, keep sqlite compat for dev
- main.py: remove run_migrations call, rely on create_all for PG
- scripts/migrate_sqlite_to_pg.py: one-shot data migration script

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/migrate_sqlite_to_pg.py

@@ -0,0 +1,130 @@
+#!/usr/bin/env python3
+"""
+Migrazione dati da SQLite → PostgreSQL per Leopost.
+Eseguire UNA SOLA VOLTA sul VPS, dopo che il container PostgreSQL è attivo
+ma prima di avviare l'app.
+
+Usage (sul VPS):
+  cd /opt/lab-leopost-full-prod
+  docker compose -f docker-compose.prod.yml up -d postgres
+  # aspetta che postgres sia healthy (10-15 sec)
+  python3 scripts/migrate_sqlite_to_pg.py \
+      --sqlite data/leopost.db \
+      --pg "postgresql://leopost:leopost_pg_2026@localhost:5433/leopost"
+"""
+
+import argparse
+import json
+import sqlite3
+import sys
+
+try:
+    import psycopg2
+    import psycopg2.extras
+except ImportError:
+    print("ERROR: psycopg2 non trovato. Installa con: pip install psycopg2-binary")
+    sys.exit(1)
+
+# Ordine di inserimento rispetta le FK
+TABLES_ORDER = [
+    "users",
+    "subscription_codes",
+    "characters",
+    "posts",
+    "affiliate_links",
+    "editorial_plans",
+    "scheduled_posts",
+    "social_accounts",
+    "comments",
+    "system_settings",
+]
+
+
+def get_sqlite_data(sqlite_path: str) -> dict[str, list[dict]]:
+    conn = sqlite3.connect(sqlite_path)
+    conn.row_factory = sqlite3.Row
+    data = {}
+    cursor = conn.cursor()
+    for table in TABLES_ORDER:
+        try:
+            cursor.execute(f"SELECT * FROM {table}")
+            rows = [dict(r) for r in cursor.fetchall()]
+            data[table] = rows
+            print(f"  SQLite {table}: {len(rows)} righe lette")
+        except sqlite3.OperationalError as e:
+            print(f"  SQLite {table}: saltata ({e})")
+            data[table] = []
+    conn.close()
+    return data
+
+
+def migrate(sqlite_path: str, pg_dsn: str):
+    print(f"\n[1/3] Lettura SQLite: {sqlite_path}")
+    data = get_sqlite_data(sqlite_path)
+
+    print(f"\n[2/3] Connessione PostgreSQL...")
+    pg = psycopg2.connect(pg_dsn)
+    pg.autocommit = False
+    cur = pg.cursor()
+
+    print(f"\n[3/3] Inserimento dati in PostgreSQL...")
+
+    # Disabilita temporaneamente i trigger di FK per inserimento sicuro
+    cur.execute("SET session_replication_role = replica;")
+
+    for table in TABLES_ORDER:
+        rows = data.get(table, [])
+        if not rows:
+            print(f"  {table}: nessuna riga, saltata")
+            continue
+
+        cols = list(rows[0].keys())
+        placeholders = ", ".join(["%s"] * len(cols))
+        col_names = ", ".join(cols)
+        sql = f"INSERT INTO {table} ({col_names}) VALUES ({placeholders}) ON CONFLICT DO NOTHING"
+
+        inserted = 0
+        for row in rows:
+            values = []
+            for col in cols:
+                v = row[col]
+                # SQLite stores JSON as string — psycopg2 needs Python objects for JSON columns
+                if isinstance(v, str) and v and v[0] in ("{", "["):
+                    try:
+                        v = json.loads(v)
+                        v = psycopg2.extras.Json(v)
+                    except json.JSONDecodeError:
+                        pass
+                values.append(v)
+            try:
+                cur.execute(sql, values)
+                inserted += 1
+            except Exception as e:
+                print(f"    WARN riga in {table}: {e} — saltata")
+
+        print(f"  {table}: {inserted}/{len(rows)} righe inserite")
+
+    # Ripristina FK e resetta le sequenze
+    cur.execute("SET session_replication_role = DEFAULT;")
+
+    print("\n  Resetting sequences PostgreSQL...")
+    for table in TABLES_ORDER:
+        cur.execute(f"""
+            SELECT setval(
+                pg_get_serial_sequence('{table}', 'id'),
+                COALESCE((SELECT MAX(id) FROM {table}), 1)
+            )
+        """)
+
+    pg.commit()
+    cur.close()
+    pg.close()
+    print("\n✓ Migrazione completata con successo.")
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--sqlite", required=True, help="Path al file SQLite (es. data/leopost.db)")
+    parser.add_argument("--pg", required=True, help="DSN PostgreSQL (es. postgresql://leopost:pass@localhost:5433/leopost)")
+    args = parser.parse_args()
+    migrate(args.sqlite, args.pg)