Add export stackable prints feature with model repository links

[Copilot]

Description

Implements the export stackable prints feature requested in #118. Users can now see stacking recommendations based on printer Z height and get direct links to Gridfinity models on MakerWorld, Printables, and Thangs.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Related Issue

Fixes #118

Changes Made

• New export service (src/services/exportService.ts): Calculates stacking recommendations based on printer Z height and component heights
• New ExportPanel component (src/components/GridfinityCalculator/ExportPanel.tsx): Displays stackable print list with expandable details
• Model repository links: Direct search links to MakerWorld, Printables, and Thangs for each baseplate/bin size
• Copy/Download options: Users can copy print list to clipboard or download as text file
• Updated Features section: Removed "Coming Soon" label from export feature

Export Panel Features

• Shows total items, print jobs, and stacking efficiency percentage
• Calculates max items per stack based on printer Z height (5mm safety margin, 20 item practical limit)
• Color-coded cards: blue for baseplates, green for half-size bins, orange for spacers

Testing

• All existing tests pass
• Added new tests for new functionality (13 tests for export service)
• Tested manually in browser
• Tested with different drawer dimensions
• Tested with custom printer settings
• Tested with half-size bins enabled/disabled

Screenshots

Export Panel with stacking instructions

Checklist

• My code follows the project's code style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have used unitMath service for all calculations (no native JS math operations)
• I have used @/ import paths consistently

Original prompt

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This section details on the original issue you should resolve

<issue_title>support for Export Stackable prints</issue_title>
<issue_description>Is there a feature to stack same prints on top of each other to same time?</issue_description>

Comments on the Issue (you are @copilot in this section)

@ntindle looking into this :) @ntindle @iq0099 how would you like to recieve this? in a download 3mf?? a link to bambu's maker world or thingiverse?

• Fixes support for Export Stackable prints #5

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