Build menu: Shift+Q/E switch tabs, G no longer picks (middle mouse does)

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

docs/DESIGN.md

@@ -79,7 +79,8 @@ Details and numbers live in the code and in `docs/systems/`.
   - Machines: fan, Refiner, Stone cutter, Silo.
   - Molds: ingot, bit, tank.
   - Build actions: drag for lines, Shift-drag for rectangles, Ctrl to replace, hold C / X and
-    drag to copy / cut, V to paste, Ctrl+Z to undo, middle mouse (or G) to pick.
+    drag to copy / cut, V to paste, Ctrl+Z to undo, middle mouse to pick,
+    Shift+Q/E to switch build tabs.
 - **Economy:**
   - The trade dock pays for anything dropped through its grate, at the market price.
   - Prices dip when you sell a lot of one thing and recover over minutes.
@@ -135,8 +136,8 @@ above, including:
   build more lines.
 - **A heap on a belt moves as one**, up to 96 grains deep, not just its bottom layer. The owner
   reports this still misbehaves (see NOTES.md).
-- **Pick** (middle mouse, also G for now) selects the piece under the cursor with its direction,
-  wall material and filter settings. The owner wants G dropped (see NOTES.md).
+- **Pick** (middle mouse) selects the piece under the cursor with its direction,
+  wall material and filter settings. G is unbound, as the owner requested.
 - **The build menu** is a bar of tabs and icon tiles along the bottom: Structure, Moving,
   Liquids, Machines, Molds. The owner wants more changes (see NOTES.md).
 - **No length limit when dragging.** Blocks out of the bot's reach become ghosts that it builds