Add panel-to-PCB mounting system with M3 standoffs

Panel alignment:
- PCB offset 10mm from panel top
- Component holes aligned: OLED@25mm, jacks@45mm, button@58mm
- 4x M3 standoff holes at corners (5,5), (35,5), (5,75), (35,75)

Updates:
- Panel SVG and spec aligned with PCB layout
- Mounting holes added to PCB (Edge.Cuts layer)
- Regenerated Gerbers with mounting holes
- Updated autoroute.py to add mounting holes automatically

DRC: 0 unconnected, 7 cosmetic errors (courtyard overlaps)

.gitignore

@@ -32,3 +32,9 @@ firmware/.pio/
 # OS
 .DS_Store
 Thumbs.db
+
+# Build artifacts
+*.dsn
+*.ses
+*.mgc
+DRC.rpt