Enhance GPU flavor scanning and update documentation

- Introduced SCAN_POOLS configuration to specify pools for GPU flavor scanning.
- Updated the `flavors` command to scan specified pools and list available GPU flavors based on `FLAVOR_PREFERENCE`.
- Revised CLI documentation to reflect changes in the `flavors` command behavior.
- Enhanced decision documentation to include details about GPU pool scanning.
- Updated setup instructions to guide users on selecting appropriate GPU pools.

src/gpu_rent/session.py

@@ -33,6 +33,7 @@ from gpu_rent.inventory import (
     resolve_flavor,
 )
 from gpu_rent.ux import print_up_preview
+from gpu_rent.pools import best_offer, format_pool_scan, scan_pools
 from gpu_rent.lock import SessionLock
 from gpu_rent.os_client import (
     KEYPAIR_NAME,
@@ -172,6 +173,21 @@ def cmd_up(
         vtype = pick_volume_type(list(iter_volume_types(conn)), cfg.gpu_rent_az)
         spot = cfg.default_spot and not no_spot
 
+        try:
+            offers = scan_pools(cfg)
+            for line in format_pool_scan(offers, cfg.flavor_preference):
+                log(line)
+            best = best_offer(offers)
+            if best and best.region != cfg.os_region_name:
+                log(
+                    f"! сейчас OS_REGION_NAME={cfg.os_region_name}, "
+                    f"а предпочтение лучше закрывается в {best.region} — "
+                    f"поставь OS_REGION_NAME={best.region} и GPU_RENT_AZ={best.region}a "
+                    f"в .env (диски ещё не созданы) и повтори up"
+                )
+        except Exception as exc:
+            log(f"скан пулов: {exc}")
+
         print_up_preview(cfg, flavors, picked=picked, spot=spot, log=log)
 
         prompt = (