docs: item 4 — add 1.5 mm hex (MK8 drive-gear set screw)

Owner-confirmed: the MK8 drive gear is locked to the motor shaft with a set
screw driven by a 1.5 mm hex. The wiki already listed three tools; this adds the
missing pieces so BOM, wiki tool list, and steps agree:
- BOM "Assembly Tools Required": add "Hex driver, 1.5 mm" (store link TODO — no
  verified 1.5 mm product URL yet).
- Build Guide Step 4: was "fit the drive pulley onto the shaft" with no set-screw
  mention; now "fit the MK8 drive gear and secure it with its set screw (1.5 mm
  hex)", snug-then-fine-tune. Renamed pulley -> gear to match the BOM.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: daniel-frenkel

docs/BOM-V2.0.md

@@ -42,4 +42,5 @@
 | Part | Qty | Description |
 | :--- | :---: | :--- |
 | Screwdriver, Phillips No. 1 | 1 | [Phillips No. 1](https://valarsystems.com/products/phillips-no-1-screw-driver). |
-| Hex driver, 2 mm | 1 | [2 mm hex driver](https://valarsystems.com/products/allen-wrench-2mm). |
+| Hex driver, 2 mm | 1 | For the M3 button-head screws — [2 mm hex driver](https://valarsystems.com/products/allen-wrench-2mm). |
+| Hex driver, 1.5 mm | 1 | For the MK8 drive-gear set screw. |

docs/wiki-Build-Guide.md

@@ -130,8 +130,8 @@ This device works on the following curtain types.
 <!-- 📷 media/build-guide/07-wallplate-buttons.png — buttons in holes, wall plate attached with 4 screws -->
 3. **Fit the buttons and close the body.** Place the buttons into their holes, then attach the wall plate to the housing using **four M3 thread-forming screws**.
 
-<!-- 📷 media/build-guide/08-drive-pulley.png — drive pulley on motor shaft -->
-4. **Attach the drive pulley.** Fit it onto the motor shaft. You'll fine-tune its position later.
+<!-- 📷 media/build-guide/08-drive-pulley.png — MK8 drive gear on motor shaft, set screw tightened with 1.5 mm hex -->
+4. **Attach the drive gear.** Fit the **MK8 drive gear** onto the motor shaft and secure it with its **set screw, using the 1.5 mm hex driver**. Snug it just enough to hold position — you'll fine-tune the position later before fully tightening.
 
 <!-- 📷 media/build-guide/09-arms.png — arm with M3×15mm button head (red), one 633ZZ bearing (green), M3 square nut (orange) -->
 5. **Assemble the two arms.** Each arm uses an **M3 × 15 mm button-head screw**, **one 633ZZ bearing (3 × 13 × 5 mm)**, and an **M3 square nut**. **On one of the two arms, also seat a third M3 square nut into its pocket now** — that pocket is inaccessible once the arms are mated, and the **M3 × 35 mm clamp screw** in Step 8 threads into this nut to pull the arm pair against the drive pulley. Build both arms the same way.