add temperature filter for warm/cool color adjustment

[priyamkarn]

Summary

Adds a new temperature filter (alias: temp) for warming or cooling images.

Implementation

• Added f_temperature
• Positive values warm the image by increasing red and decreasing blue
• Negative values cool the image by decreasing red and increasing blue
• Added temperature and temp filter registrations

Usage

imgcli -vf "temperature=0.5"
imgcli -vf "temperature=-0.5"

Testing

make
./imgcli -filters
./imgcli -y -i testsrc=128x128 -vf "temperature=0.5" warm.png
./imgcli -y -i testsrc=128x128 -vf "temperature=-0.5" cool.png

Closes #

[priyamkarn]

Hi @swperb! This PR is ready for review. Could you approve the workflow run when you get a chance?

[priyamkarn]

I have made all the required changes.

[swperb]

Thanks @priyamkarn — really clean first contribution! 🎉

I verified the math: warm (+) raises red and lowers blue, cool (−) does the reverse, green and alpha stay untouched, and extreme values clamp safely via clampb. I added the one-line README filter-list entry on top, since the original issue didn't call out the docs step — that was my oversight in the issue, not yours.

Merging now. Thanks for picking this up, and hope to see you back for another!