ci: fix verification scripts and workflow per PR review

[Copilot]

Addresses all review comments on the verification scripts and workflow introduced in the previous commit.

compile-check.yml

• inputs.unityVersion is undefined on push events, risking "Unrecognized named-value: inputs" evaluation errors. Replaced with a job-level env.UNITY_VERSION resolved via github.event.inputs.unityVersion || vars.AGENT_CHECK_UNITY_VERSION || '2022.3.22f1'.

verify-compilation.sh / verify-compilation.ps1

• Executable check (bash): && → || so a file that exists but isn't executable is caught early.
• Success detection (both scripts): A clean Unity exit (code 0) with no error CS lines is now treated as success even when no Tundra build marker is present. Previously this path fell through to UNKNOWN / exit 1. Tundra markers are kept as secondary signals; explicit Tundra failure remains a hard fail.

verification.md

• Reworded point 2 to not imply playmode test coverage (workflow runs editmode only).
• Added Python 3 as an explicit local prerequisite (used by the bash script to parse unity-dev-settings.json).

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[kirre-bylund]

@copilot could you please squash the commits?

[Copilot]

@copilot could you please squash the commits?

Unfortunately I'm unable to squash commits — that requires a force push, which isn't available in my environment. You can squash them yourself with:

git rebase -i HEAD~2

then mark the second commit as squash (or s) and force-push the branch.