docs: 3rd M3x15 button head is the curtain-pulley screw; drop phantom M3x12 flat-head

Owner-confirmed fastener map: M3x15 button head x3 = one per arm (2) + curtain
pulley (1); M3 square nut x4 = per arm (2) + clamp nut (1) + curtain pulley (1);
every nut pairs with exactly one screw.

- BOM-V2.0 Body: M3x15 button head 2 -> 3 (adds the pulley screw).
- BOM-V2.0 Curtain: DELETE "M3 x 12 mm flat head | 1" — it was the pulley screw
  misidentified; it does not exist as a separate part.
- Build-Guide pulley-end step + image: the V-groove pulley is held by an
  M3 x 15 mm button-head screw (not M3 x 12 mm flat-head), into an M3 square nut.

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

Author: daniel-frenkel

docs/BOM-V2.0.md

@@ -12,8 +12,8 @@
 | Extension cable | 1 | [Straight barrel-plug extension](https://valarsystems.com/products/barrel-plug-extension-cable). |
 | M3 × 10 mm screw, self-tapping | 8 | [Thread-forming screw](https://valarsystems.com/products/m3-x-10mm-thread-forming-screw). |
 | M3 × 35 mm screw, button head | 3 | [Arm assembly screws](https://valarsystems.com/products/m3-x-35mm-button-head-screw). |
-| M3 square nut | 3 | [Square nut](https://valarsystems.com/products/m3-square-nut). |
-| M3 × 15 mm screw, button head | 2 | [Arm screw, one per arm](https://valarsystems.com/products/m3-x-15mm-button-head-screw). |
+| M3 square nut | 3 | [Square nut](https://valarsystems.com/products/m3-square-nut) — arm nuts (2) + clamp nut (1). |
+| M3 × 15 mm screw, button head | 3 | [Arm screws (2) + curtain-pulley screw (1)](https://valarsystems.com/products/m3-x-15mm-button-head-screw). |
 | M3 × 10 mm screw, flat head | 2 | [Flat-head screw](https://valarsystems.com/products/m3-x-10mm-flat-head-screw). |
 | Gear | 1 | MK8, 5 mm bore / 9 mm OD — [buy](https://valarsystems.com/products/ropener-drive-gear). |
 | Bearing | 2 | 633ZZ, 3 mm × 13 mm × 5 mm — [buy](https://valarsystems.com/products/633zz-bearing). |
@@ -24,8 +24,7 @@
 | :--- | :---: | :--- |
 | PTFE tubing, 3 mm ID × 5 mm OD (pre-cut) | 6 | 2 × 10 mm, 2 × 40 mm, 2 × 70 mm — [buy](https://valarsystems.com/products/ptfe-tube). |
 | M3 × 10 mm screw, self-tapping | 11 | [Thread-forming screw](https://valarsystems.com/products/m3-x-10mm-thread-forming-screw). |
-| M3 square nut | 1 | [Square nut](https://valarsystems.com/products/m3-square-nut). |
-| M3 × 12 mm screw, flat head | 1 | [Flat-head screw](https://valarsystems.com/products/m3-x-12mm-flat-head-screw). |
+| M3 square nut | 1 | [Curtain-pulley nut](https://valarsystems.com/products/m3-square-nut). |
 | Zip tie | 1 | Small, 2–3 mm wide — [buy](https://valarsystems.com/products/zip-tie). |
 | V623ZZ pulley | 1 | 3 × 12 × 4 mm — [V-groove pulley](https://valarsystems.com/products/v-groove-pulley). |
 | Rope | 1 | 1.6 mm diameter — [buy](https://valarsystems.com/products/rope). |

docs/wiki-Build-Guide.md

@@ -167,8 +167,8 @@ The **PTFE tubes come pre-cut** — no cutting needed. You'll have **two of each
 <!-- 📷 media/build-guide/16-long-tubes.png — 2 long tubes placed, top plastic attached with 2 screws -->
 1. **Long tubes.** Place the **two long tubes**, then attach the top plastic using **two M3 thread-forming screws**.
 
-<!-- 📷 media/build-guide/17-pulley-end.png — pulley end: short tubes, V-groove pulley with M3×12mm flathead, square nut, M3 thread-forming -->
-2. **Pulley end.** Fit the **short tubes**, then the **V-groove pulley** held by an **M3 × 12 mm flat-head screw**, secured with a **square nut** and an **M3 thread-forming screw**.
+<!-- 📷 media/build-guide/17-pulley-end.png — pulley end: short tubes, V-groove pulley with M3×15mm button head, square nut, M3 thread-forming -->
+2. **Pulley end.** Fit the **short tubes**, then the **V-groove pulley** held by an **M3 × 15 mm button-head screw**, secured with an **M3 square nut** and an **M3 thread-forming screw**.
 
 <!-- 📷 media/build-guide/18-carriages-medium.png — 1 medium tube per carriage, top plastic over tubes, 4 side screws -->
 3. **Carriages.** Place **one medium tube** into each carriage, set the top plastic over the tubes, and drive **four M3 thread-forming screws** into the sides.