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.

pouch/yaml_io.py

@@ -59,6 +59,10 @@ def _parse_scalar(raw: str) -> Any:
         return True
     if lower == "false":
         return False
+    if raw == "[]":
+        return []
+    if raw == "{}":
+        return {}
     if raw.isdigit() or (raw.startswith("-") and raw[1:].isdigit()):
         return int(raw)
     return raw
@@ -196,7 +200,11 @@ def _dump(data: Any, indent: int = 0) -> str:
             return f"{pad}{{}}\n"
         lines: list[str] = []
         for key, value in data.items():
-            if isinstance(value, (dict, list)):
+            if isinstance(value, list) and not value:
+                lines.append(f"{pad}{key}: []")
+            elif isinstance(value, dict) and not value:
+                lines.append(f"{pad}{key}: {{}}")
+            elif isinstance(value, (dict, list)):
                 if isinstance(value, list) and value and all(isinstance(x, str) for x in value):
                     lines.append(f"{pad}{key}:")
                     for item in value: