Draw regions and paths on 3-D panels

[CSSFrancis]

Stacked on #80 (needs the model rotation for frame="world" to mean anything); retarget to main once that merges.

Why

To mark the part of a sphere a detector sees, a grain's spread on a pole sphere, or the trace of a lattice plane, a 3-D panel needs regions that sit on the surface: edges that follow the sphere, the far side visibly behind, and a choice between belonging to the object and belonging to the instrument.

What

• Plot3D.add_patch(points, *, frame="data"|"world", closed=True, geodesic=True, facecolor, edgecolor, alpha, back_alpha, linewidth, label, name) -> Patch3D, plus remove_patch, patches, and Patch3D.set(...) / .remove(). Light pushes only (no geometry resend).
• geodesic=True (default): Python joins corners by great-circle arcs about the centre of the data bounds in ≤2° steps, interpolating radius. Four corners make a detector's footprint, because a flat detector's straight edges are great circles on the sphere. Opposite points and points at the centre are rejected with a clear message.
• frame="world" uses the camera alone, so the patch stays put while set_rotation turns the data under it; "data" turns with it.
• Renderer: each patch is split at the view-space plane through the centre; the back half is drawn at back_alpha, dashed. Where a geodesic patch is cut, the fill follows the silhouette arc rather than a chord across the disc; the outline draws only the patch's own edges. Labels anchor on the patch's surface (front-most point for a full great circle), with a black/white halo picked against the label colour.
• The Kikuchi sphere example gains the detector footprint (world) and the (111) trace (data).

Tests

tests/test_plot3d/test_patches.py: geodesic edges stay on the sphere at ≤2° steps, straight/open variants, validation, set/remove as light pushes, name replacement; Playwright: a "data" patch moves under set_rotation and a "world" patch does not, and a far-side patch is drawn dimmer. test_plot3d + test_examples: 172 passed.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.85714% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.24%. Comparing base (ae048a0) to head (d0c8bd4).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
anyplotlib/plot3d/_plot3d.py	92.59%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   91.22%   91.24%   +0.02%     
==========================================
  Files          41       41              
  Lines        4910     4991      +81     
==========================================
+ Hits         4479     4554      +75     
- Misses        431      437       +6     

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