Update mechanical folder structure for multiple sub-assemblies

- Refactor mechanical/ directory to support multiple sub-assemblies instead of just enclosures
- Update mechanical/README.md with comprehensive sub-assembly organization examples
- Enhance mechanical/cad/README.md with detailed sub-assembly structure (PCB mounts, sensor housing, connector panels, cooling, etc.)
- Expand mechanical/enclosure/README.md to cover main housing, sub-enclosures, and removable panels
- Improve mechanical/stl/README.md with broader 3D printing categories including tooling, prototyping, and custom components
- Update mechanical/drawings/README.md with comprehensive technical drawing organization for all mechanical components
- Add detailed manufacturing considerations, quality control procedures, and file management guidelines
- Support complex projects with multiple mechanical sub-systems and assemblies

mechanical/cad/README.md

@@ -1,3 +1,79 @@
 # /mechanical/cad
 
-Editable CAD files (e.g., FreeCAD, Fusion360).
+Editable CAD models and assemblies for all mechanical components.
+
+## Purpose
+This directory contains the source CAD files for all mechanical components and sub-assemblies in the project. These are the master files used for design, modification, and manufacturing preparation.
+
+## Organization by Sub-Assembly
+Organize CAD files by functional sub-assemblies:
+
+```
+cad/
+├── main-assembly/              # Complete system assembly
+│   ├── system-assembly.sldasm
+│   ├── system-layout.dwg
+│   └── assembly-bom.xlsx
+├── pcb-mount/                  # PCB mounting and support
+│   ├── pcb-bracket.sldprt
+│   ├── standoffs.sldprt
+│   └── mounting-plate.sldprt
+├── sensor-housing/             # Sensor enclosures and protection
+│   ├── sensor-mount.sldprt
+│   ├── protective-cover.sldprt
+│   └── cable-gland.sldprt
+├── connector-panel/            # External interfaces
+│   ├── front-panel.sldprt
+│   ├── connector-cutouts.dxf
+│   └── panel-assembly.sldasm
+├── cooling/                    # Thermal management
+│   ├── heat-sink.sldprt
+│   ├── fan-mount.sldprt
+│   └── thermal-interface.sldprt
+└── fasteners/                  # Custom hardware
+    ├── custom-screws.sldprt
+    ├── spacers.sldprt
+    └── washers.sldprt
+```
+
+## File Types
+- **Part Files**: Individual components (.sldprt, .prt, .ipt)
+- **Assembly Files**: Multi-part assemblies (.sldasm, .asm, .iam)
+- **Drawing Files**: 2D technical drawings (.slddrw, .dwg, .idw)
+- **Neutral Formats**: STEP, IGES for cross-platform compatibility
+
+## CAD Standards
+- **Units**: Use consistent units (preferably metric)
+- **Materials**: Assign appropriate materials to all parts
+- **Properties**: Include mass, volume, and center of gravity
+- **Features**: Use parametric modeling with design intent
+- **Configurations**: Use configurations for part variations
+
+## File Naming Convention
+- Use descriptive, consistent naming
+- Include version numbers for major revisions
+- Examples:
+  - `PCB-Mount-Bracket_v2.1.sldprt`
+  - `Main-Housing-Assembly_v1.3.sldasm`
+  - `Connector-Panel-Front_Rev-C.sldprt`
+
+## Design Documentation
+- Include design intent in feature names
+- Document critical dimensions and tolerances
+- Specify manufacturing processes and materials
+- Include assembly notes and special requirements
+- Reference related electrical and thermal requirements
+
+## Version Control
+- Commit CAD files with descriptive messages
+- Tag major design milestones
+- Include PDF drawings with CAD file commits
+- Document design changes in commit messages
+- Use branching for experimental design variations
+
+## Manufacturing Preparation
+- Generate STEP files for manufacturing
+- Create technical drawings with GD&T
+- Specify surface finishes and treatments
+- Include material specifications
+- Document assembly sequences and tooling requirements