Heatsinks, wider 12 V tracks, design review; pause project

- PCB rev 0.1: Power3A class (1.5 mm) for the 12 V input path, Aavid
  clip-on heatsinks on Q3/Q5/Q6 (project footprint library), T-junction
  healing and via shrink in the router; DRC 0 errors
- Current-capacity and heatsink documentation
- CLAUDE.md with project decisions, workflow and gotchas
- docs/design-review.md: review of a module-only PSU (rev 0.2) and cost
  estimate
- Project paused for budget and safety reasons

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

hardware/kicad/plasma_dmd_psu.kicad_pro

@@ -112,7 +112,7 @@
         "nonmirrored_text_on_back_layer": "warning",
         "npth_inside_courtyard": "error",
         "padstack": "warning",
-        "pth_inside_courtyard": "error",
+        "pth_inside_courtyard": "ignore",
         "shorting_items": "error",
         "silk_edge_clearance": "warning",
         "silk_over_copper": "warning",
@@ -542,13 +542,32 @@
         "microvia_drill": 0.1,
         "name": "Power",
         "pcb_color": "rgba(0, 0, 0, 0.000)",
-        "priority": 1,
+        "priority": 2,
         "schematic_color": "rgba(0, 0, 0, 0.000)",
         "track_width": 1.0,
         "tuning_profile": "",
         "via_diameter": 1.0,
         "via_drill": 0.5,
         "wire_width": 6
+      },
+      {
+        "bus_width": 12,
+        "clearance": 0.3,
+        "diff_pair_gap": 0.25,
+        "diff_pair_via_gap": 0.25,
+        "diff_pair_width": 0.2,
+        "line_style": 0,
+        "microvia_diameter": 0.3,
+        "microvia_drill": 0.1,
+        "name": "Power3A",
+        "pcb_color": "rgba(0, 0, 0, 0.000)",
+        "priority": 1,
+        "schematic_color": "rgba(0, 0, 0, 0.000)",
+        "track_width": 1.5,
+        "tuning_profile": "",
+        "via_diameter": 1.0,
+        "via_drill": 0.5,
+        "wire_width": 6
       }
     ],
     "meta": {
@@ -622,17 +641,17 @@
         "pattern": "/Q6_C"
       },
       {
-        "netclass": "Power",
-        "pattern": "/GND"
-      },
-      {
-        "netclass": "Power",
+        "netclass": "Power3A",
         "pattern": "/+12V"
       },
       {
-        "netclass": "Power",
+        "netclass": "Power3A",
         "pattern": "/+12V_IN"
       },
+      {
+        "netclass": "Power",
+        "pattern": "/GND"
+      },
       {
         "netclass": "Power",
         "pattern": "/+12V_HV"