docs: the Action card overstated what CI enforcement does (#37)

The "GitHub Action" card on the home page said the Action is
*"enforcement in CI that a contributor cannot skip"*.

Two other places on the same page are careful about exactly this:

- the pricing note — *"the only way Commit Check blocks a merge is if
you make it a required check yourself"*
- the FAQ — *"Make the Action or the App a required status check and a
violating change cannot merge"*

So the card was the odd one out, and it is the one a reader meets first.
An Action that is not a required status check runs, reports, and the
pull request merges anyway.

The new wording keeps the contrast the card was drawing with the
pre-commit hook card above it — which a contributor genuinely *can* skip
with `--no-verify` — and states the condition for blocking a merge:

> Runs in CI whether or not the hook ran. Make it a required check and a
violation cannot merge, with per-rule outputs later steps can gate on.

Found by CodeRabbit on #36, which merged before the fix could be applied
there.

`pytest tests/` passes (10) and `mkdocs build --strict` is clean.

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Author: shenxianpeng

docs/index.md

@@ -248,8 +248,8 @@ One policy engine, five places to enforce it. Every one of them reads the same
 
     ---
 
-    Enforcement in CI that a contributor cannot skip, with per-rule outputs
-    later steps can gate on.
+    Runs in CI whether or not the hook ran. Make it a required check and a
+    violation cannot merge, with per-rule outputs later steps can gate on.
 
     [:octicons-arrow-right-24: Guide](guides/github-actions.md)