add design decisions: nomenclature, build approach, bow wall functions

docs/design-decisions.md

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+# Design Decisions
+
+## Build Approach
+
+Wooden case with salvaged laptop lid (screen + hinge) as the canopy. Approximate briefcase dimensions, with the display panel setting minimum width and depth.
+
+## Salvage Exclusions
+
+- **Webcam:** Scrapped. Proprietary pinout, not worth reverse engineering.
+- **Keyboard/trackpad:** Proprietary connectors, not reusable.
+- **RAM:** DDR3L soldered, wrong generation.
+- **SSD:** Owner repurposed.
+- **WiFi card:** Intel 7265NGW needs M.2 E-key, OPi5 base lacks it.
+
+## Case Orientation & Nomenclature
+
+User sits at the **stern**, facing the **bow**. Hinge axis runs port-to-starboard along the bow edge.
+
+### Base (wooden enclosure)
+
+| Term | Surface | Notes |
+|------|---------|-------|
+| **Deck** | Top | Keyboard, controls, SBC access |
+| **Keel** | Bottom | Sits on table |
+| **Bow** | Back edge (spine side) | Power input, heat exhaust, farthest from user |
+| **Stern** | Front edge (lip side) | User-facing, keyboard near here |
+| **Port** | Left (facing bow) | |
+| **Starboard** | Right (facing bow) | |
+
+### Canopy (laptop lid + screen)
+
+| Term | Surface |
+|------|---------|
+| **Canopy dorsal** | Outside of lid |
+| **Canopy ventral** | Screen side |
+
+### Bow Wall Functions
+
+- Power input (barrel jack or USB-C PD)
+- Exhaust fans blowing away from user
+- Heat management surface