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/long-ship/agents/openai.yaml

@@ -0,0 +1,6 @@
+interface:
+  display_name: "Long Ship"
+  short_description: "Turn an approved PRD into shipped work"
+  default_prompt: "Use $long-ship to turn this complex requirement into dependent tasks and a complete delivery flow."
+policy:
+  allow_implicit_invocation: true