Say what "the board never merges" always meant

It meant main. A phase branch is the board's own, and merging into it
is bookkeeping in the same family as committing a move — so the
absolute in AGENTS.md, and the same claim on the landing page, both
become "never merges into main". Nothing about the human gate changes;
the sentence just stops overstating it.

The rest is the section the runner needs: how a phase is started, why
the branch exists at all, what makes the beat stateless, what green
means and what halts, and who runs it when there are replicas.

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

site/templates/home.html

@@ -165,8 +165,8 @@ Task board for ~/your-repo/.task-manager/tasks
     <div class="why-reason">
       <span class="why-lead">Nothing merges without you</span>
       <span class="why-text">Finished work arrives as a PR with CI on the
-        card. bench never merges — the button stays yours, and you stop
-        being the thing everything queues behind.</span>
+        card. bench never merges into main — the button stays yours, and
+        you stop being the thing everything queues behind.</span>
     </div>
   </div>
 </section>