Let auto-build slots run their own build command under their own name

A branches.<name>.autoBuild.times entry is now either a plain HH:MM
string or an object with time, its own buildCommand, and a name, so a
nightly slot can run a fuller check than the on-commit builds. The
watcher passes the slot's command and name to the executor, persisted in
the build result — UI restarts, gittally retry, and the startup recovery
repeat a build with the command and name it originally ran under.

A named slot (e.g. master@nightly) gets its own pool: repository
grouping, retention count, branches-view row (sorted after its branch),
latest status, and permanent latest-green artifact link are keyed by the
build name, while origin lookups, gone-branch pruning, worktrees, and
Gitea links/statuses stay keyed by the real branch. Without a name,
slot builds share the branch's pool as before.

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

src/main/resources/templates/current.html

@@ -15,8 +15,8 @@
                 <span th:class="'status status-' + ${build.status}" th:text="${build.status}">running</span>
                 <span class="branch link-tools">
                     <a th:if="${build.branchUrl != null}" th:href="${build.branchUrl}" target="_blank"
-                       rel="noopener noreferrer" th:text="${build.branch}">main</a>
-                    <span th:if="${build.branchUrl == null}" th:text="${build.branch}">main</span>
+                       rel="noopener noreferrer" th:text="${build.name}">main</a>
+                    <span th:if="${build.branchUrl == null}" th:text="${build.name}">main</span>
                 </span>
                 <code>
                     <a th:if="${build.commitUrl != null}" th:href="${build.commitUrl}" target="_blank"
@@ -30,7 +30,7 @@
                             th:attr="data-artifact-key=${build.artifactKey}" title="Cancel build">× Cancel</button>
                 </span>
             </header>
-            <pre class="live-log" th:attr="aria-label='live log of ' + ${build.branch}"></pre>
+            <pre class="live-log" th:attr="aria-label='live log of ' + ${build.name}"></pre>
         </section>
     </div>
 </main>