Refine repository structure for KiCad 9 optimization

- Add dedicated /kicad/ directory with organized subdirectories for libraries, schematics, gerbers, plots, and backups
- Create comprehensive KiCad 9 library structure (symbols, footprints, 3D models)
- Add manufacturing-ready directories for production files (gerbers, drill, pick-and-place)
- Update all README files with KiCad-specific documentation and workflows
- Add KiCad-optimized .gitignore file for proper version control
- Create KICAD-PROJECT-TEMPLATE.md comprehensive usage guide
- Add hardware assembly documentation and BOM management
- Include detailed manufacturing file generation instructions
- Add docs structure with design-notes and user-manual directories
- Provide complete workflow from design to manufacturing with quality checklists

kicad/libraries/3dmodels/README.md

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+# /kicad/libraries/3dmodels
+
+Custom 3D models for your KiCad project footprints.
+
+## File Formats
+- **STEP files (`.step`)**: Preferred for mechanical accuracy and CAD integration
+- **VRML files (`.wrl`)**: Legacy format, still supported by KiCad 3D viewer
+- **WRL files (`.wrl`)**: Alternative VRML extension
+
+## Naming Convention
+- Use descriptive names matching your footprints
+- Examples:
+  - `USB-C_Receptacle.step`
+  - `STM32F4_LQFP64.step`
+  - `Header_2x10_2.54mm.wrl`
+
+## Model Guidelines
+- **Scale**: Ensure models are in millimeters (KiCad's native unit)
+- **Origin**: Position the model origin to match the footprint's origin
+- **Orientation**: Align the model with the footprint's orientation
+- **Detail Level**: Balance detail with file size for performance
+
+## File Organization
+```
+3dmodels/
+├── connectors/
+│   ├── USB-C_Receptacle.step
+│   ├── Header_2x10_2.54mm.step
+│   └── Terminal_Block_3pin.step
+├── mcu/
+│   ├── STM32F4_LQFP64.step
+│   └── ESP32_Module.step
+├── sensors/
+│   ├── BME280_LGA8.step
+│   └── MPU6050_QFN24.step
+└── passive/
+    ├── Resistor_0603.step
+    ├── Capacitor_0805.step
+    └── LED_0603.step
+```
+
+## Associating Models with Footprints
+1. Open footprint in KiCad Footprint Editor
+2. Go to **Footprint Properties**
+3. Click **3D Settings** tab
+4. Add 3D model path (use relative paths)
+5. Adjust offset, rotation, and scale if needed
+
+## Model Sources
+- **Manufacturer websites**: Often provide STEP models
+- **Component distributors**: Digi-Key, Mouser, etc.
+- **3D model libraries**: GrabCAD, 3D ContentCentral
+- **KiCad official libraries**: For standard components
+- **Custom modeling**: Create your own in CAD software
+
+## Best Practices
+- Use relative paths: `${KIPRJMOD}/kicad/libraries/3dmodels/`
+- Keep file sizes reasonable (< 1MB per model when possible)
+- Test models in KiCad 3D viewer before finalizing
+- Document model sources and modifications
+- Version control important custom models