Separate queue wait from build duration

BuildResult gains runningSince, set when a build leaves the queue; the
recorded duration now measures pure build time from that point, so build
runtimes can be tracked without queue wait. A build cancelled while still
queued records neither. The UI shows the live wait time in italics while
pending and switches to the real build time once the build runs; the Gitea
"after mm:ss" descriptions now also report pure build time.

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

src/main/resources/templates/builds.html

@@ -24,7 +24,7 @@
                 <td class="empty" colspan="7" th:text="${emptyMessage}">No builds recorded yet.</td>
             </tr>
             <tr th:each="row : ${rows}"
-                th:attr="data-artifact-key=${row.artifactKey},data-branch=${row.branch},data-started-at=${row.startedAtIso},data-status=${row.status}">
+                th:attr="data-artifact-key=${row.artifactKey},data-branch=${row.branch},data-started-at=${row.startedAtIso},data-running-since=${row.runningSinceIso},data-status=${row.status}">
                 <td data-label="Status">
                     <span th:class="'status status-' + ${row.status}" th:text="${row.status}">success</span>
                 </td>