Add 12V rail for N64 + silkscreen updates

Add a 12V rail for the N64 slot. This is not currently implemented, but as the six-slot adapter is the hardest of the 2 boards to upgrade having it now will save some effort for anyone wanting it in the future. It also makes it easier to externally supply 12V by attaching clips to the 12V and GND header pins.

Also improved the silkscreen a bit to match the main PCB.

hardware/six_slot_adapter/six_slot_adapter.kicad_pro

@@ -1,5 +1,6 @@
 {
   "board": {
+    "3dviewports": [],
     "design_settings": {
       "defaults": {
         "board_outline_line_width": 0.09999999999999999,
@@ -130,7 +131,8 @@
       "zones_allow_external_fillets": false,
       "zones_use_no_outline": true
     },
-    "layer_presets": []
+    "layer_presets": [],
+    "viewports": []
   },
   "boards": [],
   "cvpcb": {
@@ -314,18 +316,23 @@
     "rule_severities": {
       "bus_definition_conflict": "error",
       "bus_entry_needed": "error",
-      "bus_label_syntax": "error",
       "bus_to_bus_conflict": "error",
       "bus_to_net_conflict": "error",
+      "conflicting_netclasses": "error",
       "different_unit_footprint": "error",
       "different_unit_net": "error",
       "duplicate_reference": "error",
       "duplicate_sheet_names": "error",
+      "endpoint_off_grid": "warning",
       "extra_units": "error",
       "global_label_dangling": "warning",
       "hier_label_mismatch": "error",
       "label_dangling": "error",
       "lib_symbol_issues": "warning",
+      "missing_bidi_pin": "warning",
+      "missing_input_pin": "warning",
+      "missing_power_pin": "error",
+      "missing_unit": "warning",
       "multiple_net_names": "warning",
       "net_not_bus_member": "warning",
       "no_connect_connected": "warning",
@@ -335,6 +342,7 @@
       "pin_to_pin": "warning",
       "power_pin_not_driven": "error",
       "similar_labels": "warning",
+      "simulation_model_issue": "error",
       "unannotated": "error",
       "unit_value_mismatch": "error",
       "unresolved_variable": "error",
@@ -352,7 +360,7 @@
   "net_settings": {
     "classes": [
       {
-        "bus_width": 12.0,
+        "bus_width": 12,
         "clearance": 0.2,
         "diff_pair_gap": 0.25,
         "diff_pair_via_gap": 0.25,
@@ -366,10 +374,10 @@
         "track_width": 0.3,
         "via_diameter": 0.8,
         "via_drill": 0.4,
-        "wire_width": 6.0
+        "wire_width": 6
       },
       {
-        "bus_width": 12.0,
+        "bus_width": 12,
         "clearance": 0.2,
         "diff_pair_gap": 0.25,
         "diff_pair_via_gap": 0.25,
@@ -378,22 +386,29 @@
         "microvia_diameter": 0.3,
         "microvia_drill": 0.1,
         "name": "Power",
-        "nets": [
-          "GND",
-          "VCC"
-        ],
         "pcb_color": "rgba(0, 0, 0, 0.000)",
         "schematic_color": "rgba(0, 0, 0, 0.000)",
         "track_width": 0.6,
         "via_diameter": 0.8,
         "via_drill": 0.4,
-        "wire_width": 6.0
+        "wire_width": 6
       }
     ],
     "meta": {
-      "version": 2
+      "version": 3
     },
-    "net_colors": null
+    "net_colors": null,
+    "netclass_assignments": null,
+    "netclass_patterns": [
+      {
+        "netclass": "Power",
+        "pattern": "GND"
+      },
+      {
+        "netclass": "Power",
+        "pattern": "VCC"
+      }
+    ]
   },
   "pcbnew": {
     "last_paths": {
@@ -409,6 +424,8 @@
   "schematic": {
     "annotate_start_num": 0,
     "drawing": {
+      "dashed_lines_dash_length_ratio": 12.0,
+      "dashed_lines_gap_length_ratio": 3.0,
       "default_bus_thickness": 12.0,
       "default_line_thickness": 6.0,
       "default_text_size": 50.0,
@@ -442,7 +459,11 @@
     "page_layout_descr_file": "",
     "plot_directory": "",
     "spice_adjust_passive_values": false,
+    "spice_current_sheet_as_root": false,
     "spice_external_command": "spice \"%I\"",
+    "spice_model_current_sheet_as_root": true,
+    "spice_save_all_currents": false,
+    "spice_save_all_voltages": false,
     "subpart_first_id": 65,
     "subpart_id_separator": 0
   },