fix: indent docstring body in help paste output

Command name stays flush-left, docstring lines indented 4 spaces.
Plugin descriptions in the full reference also indented under headers.
Adds test_help_paste_body_indented to verify formatting.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/core.py

@@ -9,14 +9,18 @@ from derp.plugin import command
 
 
 def _build_cmd_detail(handler, prefix: str) -> str:
-    """Extract and format a command's docstring into a detail block."""
+    """Extract and format a command's docstring into a detail block.
+
+    Command name anchors the left edge; docstring body is indented 4 spaces.
+    """
     doc = textwrap.dedent(handler.callback.__doc__ or "").strip()
     if not doc:
         return ""
     header = f"{prefix}{handler.name}"
     if handler.help:
         header += f" -- {handler.help}"
-    return f"{header}\n{doc}"
+    indented = textwrap.indent(doc, "    ")
+    return f"{header}\n{indented}"
 
 
 async def _paste(bot, text: str) -> str | None:
@@ -108,7 +112,7 @@ async def cmd_help(bot, message):
         desc = (getattr(mod, "__doc__", "") or "").split("\n")[0].strip() if mod else ""
         header = f"[{plugin_name}]"
         if desc:
-            header += f"  {desc}"
+            header += f"\n    {desc}"
         cmd_lines = []
         for cmd_name in plugins[plugin_name]:
             h = bot.registry.commands[cmd_name]
@@ -120,7 +124,7 @@ async def cmd_help(bot, message):
                 if h.help:
                     line += f" -- {h.help}"
                 cmd_lines.append(line)
-        blocks.append(header + "\n" + "\n\n".join(cmd_lines))
+        blocks.append(header + "\n\n" + "\n\n".join(cmd_lines))
     if blocks:
         url = await _paste(bot, "\n\n".join(blocks))
         if url: