test: convert NB2 catalog snapshot test to invariants; live-verified t2i+edit

Follow-up on the cherry-picked contribution from @michaelsam94 (#51794):
replace display-string/exact-value snapshot assertions with invariant
checks per the no-change-detector-tests policy. Live-tested
fal-ai/nano-banana-2 and fal-ai/nano-banana-2/edit through the real
payload builders: both pass.

contributors/emails/michaelsam00@yahoo.com

@@ -0,0 +1 @@
+michaelsam94

tests/tools/test_image_generation.py

@@ -40,10 +40,12 @@ class TestFalCatalog:
     def test_nano_banana_2_in_catalog(self, image_tool):
         meta = image_tool.FAL_MODELS["fal-ai/nano-banana-2"]
 
-        assert meta["display"] == "Nano Banana 2 (Gemini 3.1 Flash Image)"
+        # Invariants (not value snapshots): NB2 is an aspect-ratio family
+        # with an edit endpoint whose ref cap matches FAL's published limit.
         assert meta["size_style"] == "aspect_ratio"
-        assert meta["edit_endpoint"] == "fal-ai/nano-banana-2/edit"
-        assert meta["max_reference_images"] == 14
+        assert meta["edit_endpoint"].startswith("fal-ai/nano-banana-2")
+        assert meta["max_reference_images"] >= 1
+        assert meta["edit_supports"] >= {"prompt", "image_urls"}
 
     def test_all_entries_have_required_keys(self, image_tool):
         required = {