Make the skill runbook limits a general setting

The longest runbook a skill may save and how much of it load_skill hands
back are now set on Settings > General (skill_body_max_chars,
skill_body_shown_chars), defaulting to AppData.SkillBodyMaxChars and
SkillBodyShownChars. Saving, confirming and proposing a skill check the
install's limit; a skill saved before it was lowered can still be toggled.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/functions/backend/db/extensions/assert-skill-body-fits.ts

@@ -0,0 +1,20 @@
+import { grabSkillBodyMaxChars } from "../app-settings/grab-skill-limits";
+import AppError from "@/src/utils/app-error";
+
+type Params = {
+    body: string;
+};
+
+/**
+ * Refuses a runbook longer than the install's limit (Settings > General).
+ * The request schemas only hold the ceiling, since the limit is a setting.
+ */
+export default async function assertSkillBodyFits({ body }: Params) {
+    const max = await grabSkillBodyMaxChars();
+
+    if (body.length > max) {
+        throw new AppError(
+            `Keep the runbook under ${max} characters (it has ${body.length}). A super admin can raise the limit on Settings > General.`,
+        );
+    }
+}