Add per-service system prompts with AI Settings tab view

Each feature service owns its system prompt in its config JSON on the
shared volume. The AI Settings page now has General and System Prompts
tabs — admins can view and edit any service's prompts at runtime with
changes taking effect within 30 s (config cache TTL).

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

frontend/src/api/client.ts

@@ -219,3 +219,23 @@ export const updateDocumentLimits = (max_pdf_mb: number) =>
 
 export const getDocumentLimits = () =>
   api.get<Record<string, unknown>>("/settings/documents/limits").then((r) => r.data);
+
+// --- System Prompts (admin only) ---
+export interface ServiceSystemPrompt {
+  label: string;
+  system: string;
+  user_template: string;
+}
+
+export type SystemPromptsData = Record<string, ServiceSystemPrompt>;
+
+export const getSystemPrompts = () =>
+  api.get<SystemPromptsData>("/settings/system-prompts").then((r) => r.data);
+
+export const updateSystemPrompt = (
+  serviceId: string,
+  data: { system: string; user_template: string }
+) =>
+  api
+    .patch<SystemPromptsData>(`/settings/system-prompts/${serviceId}`, data)
+    .then((r) => r.data);