Update mechanical component links to use nightly-mechanical release assets

Replaces broken preview branch links with direct release download URLs.
Adds engraving PDF for KNOT-HOUSING which is now available as a release asset.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: SukuWc

README.md

@@ -16,9 +16,9 @@ You can find more info on the [website](https://intech.studio/shop/knot) or in t
 
 | Component                 | Part number          | Type       | Preview | Links        |
 |---------------------------|----------------------|------------|---------|--------------|
-| Aluminum housing          | KNOT-HOUSING         | Fabricated | <img src="../preview/Preview/Mechanical/KNOT-HOUSING.png?raw=true" width="100"> | [[step]](../preview/Preview/Mechanical/KNOT-HOUSING.step) [[stl]](../preview/Preview/Mechanical/KNOT-HOUSING.stl) [[pdf]](../preview/Preview/Mechanical/KNOT-HOUSING_Drawing.pdf) |
-| Aluminum front panel      | KNOT-FRONT           | Fabricated | <img src="../preview/Preview/Mechanical/KNOT-FRONT.png?raw=true" width="100"> | [[step]](../preview/Preview/Mechanical/KNOT-FRONT.step) [[stl]](../preview/Preview/Mechanical/KNOT-FRONT.stl) [[pdf]](../preview/Preview/Mechanical/KNOT-FRONT_Drawing.pdf) |
-| Aluminum back panel       | KNOT-BACK            | Fabricated | <img src="../preview/Preview/Mechanical/KNOT-BACK.png?raw=true" width="100"> | [[step]](../preview/Preview/Mechanical/KNOT-BACK.step) [[stl]](../preview/Preview/Mechanical/KNOT-BACK.stl) [[pdf]](../preview/Preview/Mechanical/KNOT-BACK_Drawing.pdf) |
+| Aluminum housing          | KNOT-HOUSING         | Fabricated | <img src="https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-HOUSING.png" width="100"> | [[step]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-HOUSING.step) [[stl]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-HOUSING.stl) [[pdf]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-HOUSING_Drawing.pdf) [[engraving]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-HOUSING_Engraving.pdf) |
+| Aluminum front panel      | KNOT-FRONT           | Fabricated | <img src="https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-FRONT.png" width="100"> | [[step]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-FRONT.step) [[stl]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-FRONT.stl) [[pdf]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-FRONT_Drawing.pdf) |
+| Aluminum back panel       | KNOT-BACK            | Fabricated | <img src="https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-BACK.png" width="100"> | [[step]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-BACK.step) [[stl]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-BACK.stl) [[pdf]](https://github.com/intechstudio/knot/releases/download/nightly-mechanical/KNOT-BACK_Drawing.pdf) |
 
 ### Nightly Firmware version