Feat: add a new agent: Google Anti Gravity

[TCoherence]

Background

Recently Google just release their new AI IDE - Anti Gravity with Gemini 3.0 Pro! I noticed that we already have 2 threads talking about this #1213 and #1217
So this is the PR to officially support this!

AI disclosure

This code is mainly done by using Anti Gravity with Gemini 3.0 Pro, with some manual fixes

Test Screenshot

Used .github/workflows/scripts/create-release-packages.sh script to generate a local release package and manully copied it to local branch to test it out, the result is as follows:

[TCoherence]

Hey @localden Just added another new agent for Anti Gravity. Please let me know if it looks good to you

[sakshamnanda]

I tried your PR, the specify init doesn't work on the new antigravity update, as agy command is not decoupled anymore to outside terminals.

[TCoherence]

I tried your PR, the specify init doesn't work on the new antigravity update, as agy command is not decoupled anymore to outside terminals.

@sakshamnanda The specify init command only pulls packages release officially. I actually have another separate PR to add a separate option "--template-file" in the "specify-cli" so that you can init from a specific package. Check this out: #1057

[sakshamnanda]

I tried your PR, the specify init doesn't work on the new antigravity update, as agy command is not decoupled anymore to outside terminals.

@sakshamnanda The specify init command only pulls packages release officially. I actually have another separate PR to add a separate option "--template-file" in the "specify-cli" so that you can init from a specific package. Check this out: #1057

I used this command to use your branch to initialise, and that's how I got the error.
In the official specify the agy is not even in the packages.
uvx --from "git+https://github.com/TCoherence/github-spec-kit@new_agent/antigravity" specify init .

[kvcrajan]

I appreciate for the quick turn-around, however I would like have this change merged with README update and released as template just like for other IDEs. Hope to see that soon. Great Job and Thank you again!

[TCoherence]

I tried your PR, the specify init doesn't work on the new antigravity update, as agy command is not decoupled anymore to outside terminals.

@sakshamnanda The specify init command only pulls packages release officially. I actually have another separate PR to add a separate option "--template-file" in the "specify-cli" so that you can init from a specific package. Check this out: #1057

I used this command to use your branch to initialise, and that's how I got the error. In the official specify the agy is not even in the packages. uvx --from "git+https://github.com/TCoherence/github-spec-kit@new_agent/antigravity" specify init .

@sakshamnanda For current specify command, it's forced to pull packages from the offical release, you can check it out in __init__.py. Here is a quick screenshot from Gemini's response: