ci(github): consolidate test and lint into single workflow

[vmaerten]

Summary

• Add dedicated build job to verify compilation across Go versions
• Simplify test job by using go-task/setup-task action instead of manual build
• Improve workflow readability with descriptive step names and emojis
• Reorder steps to follow checkout-first convention

Why

The previous workflow had some issues:

1. Build verification was implicit - Tests would fail if the build failed, but there was no explicit build check. Now we have a dedicated build job that runs in parallel with tests.
2. Manual build in test job was redundant - Each test job was building the binary manually with go build -o ./bin/task. By using the official go-task/setup-task action, we leverage a pre-built Task binary and simply run task test.
3. Inconsistent step ordering - Some jobs had setup-go before checkout, which is unconventional. Now all jobs follow the standard checkout → setup → action pattern.
4. Poor readability - Steps had minimal or no names. Added descriptive names with emojis to make the workflow easier to scan in the GitHub Actions UI.

Test plan

• Verify all CI jobs pass on this branch
• Confirm build job correctly tests both Go 1.24.x and 1.25.x
• Check that test job still runs on all three platforms (ubuntu, macos, windows)