Epic 108: add computational photography and panorama

[rsasaki0109]

Summary

• add gray-world balance and aligned exposure fusion
• add bounded pairwise panorama canvas with explicit origin and feather blending
• compose panorama estimation with robust homography
• expose Python APIs and OpenCV warp parity receipt

Validation

• cargo test -p spatialrust-vision --features full (92 + 10 passed)
• cargo clippy -p spatialrust-vision --no-default-features --features photography --no-deps -- -D warnings
• cargo bench -p spatialrust-vision --features photography --bench photography --no-run
• pytest crates/spatialrust-py/tests
• OpenCV photography comparison: pass
• cargo test -p spatialrust-platform