Add standalone compass() function

[joa-quim]

Summary

• Add compass() / compass!() convenience function that wraps basemap for drawing directional and magnetic compass roses
• Auto-selects -Td (directional) vs -Tm (magnetic) based on whether dec kwarg is provided
• When called standalone without region/proj, creates a paper-coordinates canvas sized to fit the rose automatically
• All compass sub-options (anchor, width, fancy, dec, annot, rose_primary, etc.) are top-level kwargs
• Uses the Dict-based dispatch pattern (no kwargs in the main function) to avoid recompilation

Test plan

• Standalone directional rose with auto canvas/centering
• Standalone with labels, anchor, explicit paper coords
• Standalone with explicit R/J (user-controlled positioning)
• Magnetic compass with dec, annot, rose_primary/secondary
• Overlay mode (compass!) reusing existing plot R/J
• Default frame=:none (no axes drawn)

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.45455% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.86%. Comparing base (53991bb) to head (8fdf2e6).

Files with missing lines	Patch %	Lines
src/compass.jl	95.45%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1917      +/-   ##
==========================================
+ Coverage   85.82%   85.86%   +0.03%     
==========================================
  Files         185      186       +1     
  Lines       27467    27511      +44     
==========================================
+ Hits        23573    23621      +48     
+ Misses       3894     3890       -4     

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