Add drawing reference generation templates for pencil drawing

[attorri]

This PR adds a drawing reference generation system for artists working with pencil and traditional media.

Changes

New Templates Added:

• pencil_drawing - Adaptive drawing reference generator with structural information
• gesture_drawing - Movement and gesture capture for quick studies
• shapes_study - Basic geometric form construction
• contour_drawing - Edge and form observation exercises
• value_study - Light and shadow rendering studies

MCP Integration:

• Added MCP prompt handlers for all drawing templates in server.py
• Natural language routing supports simple requests like "I want to draw a cat"
• All parameters properly aligned between templates and MCP functions

Design

The templates generate clean line art showing:

• Shape construction and breakdown
• Proportion relationships
• Contours and construction lines
• Volume and dimensional information

Supports multiple skill levels from beginner to advanced.

Testing

• Verified JSON validity of templates.json
• Confirmed Python syntax validity in server.py
• All MCP functions fully aligned with template parameters