Show the command a build actually runs on its artifact page

The artifact page read `branches.<branch>.buildCommand` from the primary
config only, so for a named build on a branch with its own config it showed
a command that build never ran — on vm4006 it showed the host config's
command for a build that ran the branch definition's `pitestFull`.

Resolving "what does this build run" now has one implementation,
`GitTallyConfig.buildSettings(branch, build)`: the branch entry with the
build definition's overrides applied last. The executor uses it, and the
page resolves it against the branch layer committed at the build's own
commit — the same inputs the executor had.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/main/resources/templates/artifact.html

@@ -39,7 +39,7 @@
             <li>Started: <span th:text="${result.startedAt}">2026-07-07 12:00</span>
                 <th:block th:if="${result.duration != ''}">— Duration: <span th:text="${result.duration}">1:23</span></th:block>
             </li>
-            <li th:if="${buildCommand != null}">Build command (as currently configured):<br>
+            <li th:if="${buildCommand != null}">Build command (as configured for this build):<br>
                 <code th:text="${buildCommand}">./gradlew test</code>
             </li>
         </ul>