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/utils/extension-option-value.ts

@@ -1,7 +1,7 @@
 import type { BotExtension } from "@/src/types";
 
 /**
- * An MCP server or tool as one select value (`mcp:3`), and back.
+ * An MCP server, tool or skill as one select value (`mcp:3`), and back.
  */
 export function extensionOptionValue({ kind, id }: { kind: BotExtension["kind"]; id: number }) {
     return `${kind}:${id}`;
@@ -10,7 +10,7 @@ export function extensionOptionValue({ kind, id }: { kind: BotExtension["kind"];
 export function parseExtensionOptionValue({ value }: { value: string }) {
     const [kind, id] = value.split(":");
 
-    if ((kind != "mcp" && kind != "tool") || !Number(id)) return null;
+    if ((kind != "mcp" && kind != "tool" && kind != "skill") || !Number(id)) return null;
 
     return { kind: kind as BotExtension["kind"], id: Number(id) };
 }