feat: rename bugfix-ship/requirement-flow to short-ship/long-ship with shared ship records

short-ship and long-ship share one ship-id record under .pouch/ship/<id>/.
specifier writes PRDs into spec/; delivery-loop appends evidence pointers.
Old names stay as deprecation stubs so existing installs keep working.

skills/specifier/templates/prd.template.html

@@ -30,7 +30,7 @@
 <main>
 <article>
   <header>
-    <p class="meta"><span class="badge">Feature: {{feature_id}}</span><span class="badge">PRD: {{revision}}</span><span class="badge status">状态：{{status}}</span></p>
+    <p class="meta"><span class="badge">Ship: {{ship_id}}</span><span class="badge">PRD: {{revision}}</span><span class="badge status">状态：{{status}}</span></p>
     <h1>{{feature_title}}</h1>
     <p>{{one_sentence_summary}}</p>
     <p class="muted">生成时间：{{generated_at}} · 基于版本：{{changed_from}}</p>