add port layout and video output decisions

- Mechanical HDMI A/B switch for internal/external display toggle
- DisplayLink rejected: no ARM drivers exist
- 10-port layout split across 4 surfaces
- Port side: 4x USB-A, 1x USB-C data, 1x USB-C PD out
- Starboard: Ethernet, HDMI out, 3.5mm audio
- Bow: USB-C power input + fan exhaust
- Stern: handle, SD reader, Kensington lock
- Updated BOM with HDMI switch, panel-mount cables, SD reader
- Cost estimate now ~58

README.md

@@ -15,6 +15,8 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 5 SBC
 - [x] Build approach: wooden case + salvaged lid canopy
 - [x] Input device: ThinkPad TrackPoint keyboard
 - [x] Power system: IP5389 board + 18650 cells (preliminary)
+- [x] Video output: mechanical HDMI A/B switch
+- [x] Port layout defined (10 ports + SD reader + Kensington)
 - [ ] Case design (dimensions, internal layout)
 - [ ] Power system board selection and testing
 - [ ] Bow wall design (power input, fan exhaust)
@@ -57,6 +59,7 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 5 SBC
 - [Parts List](docs/parts-list.md) - Bill of materials with costs
 - [Design Decisions](docs/design-decisions.md) - Build approach, nomenclature, layout
 - [Power System](docs/power-system.md) - IP5389 battery management decision
+- [Port Layout](docs/port-layout.md) - External port placement and allocation
 
 ## Quick Reference
 
@@ -80,8 +83,9 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 5 SBC
 |----------|------|
 | SBC | ~$104 |
 | Display controller | ~$24 |
-| Storage (SD + hub + enclosure) | ~$32-44 |
-| Power system (board + cells + fuse + charger) | ~$32-56 |
-| **Subtotal** | **$206-230** |
+| Storage (SD + hub + enclosure) | ~$34 |
+| Power system (board + cells + fuse + charger) | ~$44 |
+| HDMI switch + panel cables + SD reader | ~$33 |
+| **Subtotal** | **~$258** |
 
 (Excludes case materials and misc hardware. Battery included in power system.)