Give bots skills: runbooks they load when a job matches

A skill is a runbook: a name, a unique slug, a one-line description of when
it applies, and the markdown body. A run only ever sees the slug and
description (one load_skill tool carries them), and reads the whole body
only when it calls the tool, so a long runbook costs nothing until needed.

Skills are the third extension kind beside MCP servers and custom tools, on
the same botExtensionsSql path, so per-bot, per-workspace and all-bots
grants work the same way, and attachDefaultExtensions hands an every-bot
skill to new bots. load_skill is a reserved tool name, so a custom tool
cannot shadow it, and a built-in wins a clash.

Managed on Settings > Skills; ExtensionRow links each kind to its own page
and a skill never reports a failure, since nothing connects or runs.

src/pages/admin/bots/[bot_id]/(partials)/composer-tool-row.tsx

@@ -17,8 +17,9 @@ type Props = {
 };
 
 /**
- * One MCP server or tool the bot can use here, in the composer's tools
- * modal. One that isn't working says so, one that's off is struck out.
+ * One MCP server, tool or skill the bot can use here, in the composer's
+ * tools modal. One that isn't working says so, one that's off is struck
+ * out. A skill has nothing to connect or run, so it never reports one.
  */
 export default function ComposerToolRow({ item, busy, onRemove }: Props) {
     const Icon = extensionIcon({ kind: item.kind });
@@ -27,11 +28,13 @@ export default function ComposerToolRow({ item, busy, onRemove }: Props) {
         item.source == "workspace" ? "From this workspace" : "",
         !item.enabled
             ? "Off for every bot"
-            : item.state == "error"
-              ? "Not working"
-              : item.state == "untested"
-                ? "Not checked yet"
-                : "",
+            : item.kind == "skill"
+              ? ""
+              : item.state == "error"
+                ? "Not working"
+                : item.state == "untested"
+                  ? "Not checked yet"
+                  : "",
     ].filter(Boolean);
 
     return (