feat: support GIF image decoding

[ganeshmshetty]

Summary

• Register Go's standard library _ "image/gif" format decoder in internal/imageutil.
• Allow gif format in Decode, enabling both static and animated GIFs (using frame 0 for analysis).
• Add rose.gif fixture (28 KB) generated from rose.png to automatically exercise multipart, raw, and truncated test coverage across fixtures_test.go.
• Add unit tests in image_test.go covering static palette decoding and multi-frame animated GIF decoding.
• Update README.md and CONTRIBUTING.md to reflect GIF format support.

Validation

• make test passes with all packages green (cmd/autogravity, internal/imageutil, internal/gravity, internal/facedetection, internal/saliency).
• Standard library only — introduces zero new third-party dependencies, CGO requirements, or Dockerfile modifications.

[appwrite]

Autogravity

Project ID: 6a9e5d640016fa6fb653

Sites (1)

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Tip

Storage files get ClamAV malware scanning and encryption by default

[greptile-apps]

Confidence Score: 5/5

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

Summary

• Allows GIF input through the existing validated image decoding path.
• Verifies static GIF decoding and observable first-frame behavior for animated GIFs.
• Adds a GIF fixture to existing integration-style image coverage.

_{Reviews (2) · Last reviewed commit: "test: verify animated GIF first-frame se..."}

[ganeshmshetty]

Hey I wanted to say this autogravity is a simple but great feature for someone to have!!
I noticed that this doesn't support gif. So this is slight addition to the already supporting image formats that my agent made.
Working: The first frame of the gif is taken as the reference for pin pointing the focal point.

I also noticed how multiple focal point in a same image was managed and I think it might be worth adding a rich api to handle these kind of issues, but also saw there was a pr referring to the same issue which made me think twice.