Fix focal points between separated salient regions

[TorstenDittmann]

Summary

• group high-saliency pixels into 8-connected regions
• select the region with the greatest integrated saliency
• calculate the weighted focal point only within that region
• document the updated focal-point behavior
• add regression coverage for separated subjects with equal peak confidence

This prevents two separated subjects from averaging to a focal point in empty space between them.

Before and after

The supplied example changes from gravity=(0.4705, 0.4784) to gravity=(0.0770, 0.4788), selecting the stronger left-dog region.

Validation

• go test ./...
• ONNXRUNTIME_LIB=/path/to/libonnxruntime.dylib go test -tags=integration ./cmd/autogravity
• manually verified the supplied image through POST /analyze

[greptile-apps]

Greptile Summary

The PR changes focal-point calculation to select the 8-connected salient region with the greatest integrated saliency before calculating its weighted centroid.

• Adds connected-component selection above half the peak activation.
• Preserves peak-based confidence and center fallback behavior.
• Documents the updated focal-point semantics.
• Adds regression coverage for separated subjects and diagonal connectivity.

Confidence Score: 5/5

The PR appears safe to merge; no outstanding correctness, security, or repository-rule issues remain.

The diagonal-connectivity regression fully addresses the resolved previous finding, and the changes since the previous review introduce no actionable new issue.

Important Files Changed

Filename	Overview
internal/gravity/gravity.go	Implements thresholded 8-connected component discovery and computes the focal point from the strongest component.
internal/gravity/gravity_test.go	Covers separated salient subjects, within-component weighting, and the previously requested diagonal-connectivity behavior.
README.md	Documents selection of the connected salient region with the greatest total saliency.
docs/src/lib/site.ts	Updates site metadata to describe the strongest-region focal-point behavior.
docs/src/routes/index.tsx	Updates public endpoint documentation to match the revised algorithm.

_{Reviews (3): Last reviewed commit: "test: cover diagonal saliency connectivi..." | Re-trigger Greptile}