feat(command): add /skill slash command to list enabled skills

- Register /skill in BUILTIN_COMMAND_SPECS with wrench icon
- Add cmd_skill handler that lists skill names and descriptions
- Disabled skills are excluded from the output
- Add 6 tests covering empty list, names/descriptions, disabled
  filtering, fallback description, markdown output, and router
  registration

nanobot/command/builtin.py

@@ -98,6 +98,12 @@ BUILTIN_COMMAND_SPECS: tuple[BuiltinCommandSpec, ...] = (
         "Revert memory to a previous Dream snapshot.",
         "undo-2",
     ),
+    BuiltinCommandSpec(
+        "/skill",
+        "List skills",
+        "List all enabled skills available to the agent.",
+        "wrench",
+    ),
     BuiltinCommandSpec(
         "/help",
         "Show help",
@@ -642,6 +648,25 @@ async def cmd_pairing(ctx: CommandContext) -> OutboundMessage:
     )
 
 
+async def cmd_skill(ctx: CommandContext) -> OutboundMessage:
+    """List all enabled skills (name and description only)."""
+    loop = ctx.loop
+    skills = loop.context.skills.list_skills(filter_unavailable=False)
+    if not skills:
+        content = "No skills available."
+    else:
+        lines = [f"Available skills ({len(skills)}):", ""]
+        for entry in skills:
+            desc = loop.context.skills._get_skill_description(entry["name"])
+            lines.append(f"- **{entry['name']}** — {desc}")
+        content = "\n".join(lines)
+    return OutboundMessage(
+        channel=ctx.msg.channel,
+        chat_id=ctx.msg.chat_id,
+        content=content,
+        metadata=dict(ctx.msg.metadata or {}),
+    )
+
 async def cmd_help(ctx: CommandContext) -> OutboundMessage:
     """Return available slash commands."""
     return OutboundMessage(
@@ -681,6 +706,7 @@ def register_builtin_commands(router: CommandRouter) -> None:
     router.prefix("/dream-log ", cmd_dream_log)
     router.exact("/dream-restore", cmd_dream_restore)
     router.prefix("/dream-restore ", cmd_dream_restore)
+    router.exact("/skill", cmd_skill)
     router.exact("/help", cmd_help)
     router.exact("/pairing", cmd_pairing)
     router.prefix("/pairing ", cmd_pairing)