Add verbose flag, WireViz dev dep, and rendered diagram examples

- Gate model/value heuristic output behind --verbose/-v flag (quiet by default)
- Add wireviz>=0.4 as dev dependency for roundtrip render tests
- Generate SVG/PNG diagram renders for inter_module, single_module, hierarchical
- Embed rendered diagrams in README with layout optimization callout

tests/test_netlist_parser.py

@@ -209,16 +209,41 @@ X1 NET1 NET2 NET3 NET4 small
         assert "extra nodes" in captured.err
 
     def test_model_value_heuristic_warning(self, capsys):
-        """I6: The model/value heuristic should warn when it triggers."""
-        text = """\
+        """I6: The model/value heuristic should warn when verbose is on."""
+        from spice2wireviz.parser import netlist as netlist_module
+
+        original = netlist_module.verbose
+        try:
+            netlist_module.verbose = True
+            text = """\
 .subckt test A B
 J1 A B SOME_MODEL
 .ends test
 """
-        parse_netlist(text)
-        captured = capsys.readouterr()
-        assert "SOME_MODEL" in captured.err
-        assert "model/value" in captured.err
+            parse_netlist(text)
+            captured = capsys.readouterr()
+            assert "SOME_MODEL" in captured.err
+            assert "model/value" in captured.err
+        finally:
+            netlist_module.verbose = original
+
+    def test_model_value_heuristic_quiet_by_default(self, capsys):
+        """The model/value heuristic should be silent when verbose is off."""
+        from spice2wireviz.parser import netlist as netlist_module
+
+        original = netlist_module.verbose
+        try:
+            netlist_module.verbose = False
+            text = """\
+.subckt test A B
+J1 A B SOME_MODEL
+.ends test
+"""
+            parse_netlist(text)
+            captured = capsys.readouterr()
+            assert "model/value" not in captured.err
+        finally:
+            netlist_module.verbose = original
 
     def test_duplicate_refs_both_parsed(self):
         """S3: Duplicate reference designators should both be parsed."""