feat(ai): make agent turn limit configurable

apps/desktop/src/lib/ai/maxAgentTurns.ts

@@ -0,0 +1,14 @@
+// Mirrors DEFAULT/MIN/MAX_MAX_AGENT_TURNS in crates/dbx-core/src/agent_loop.rs.
+// The backend clamp remains the source of truth for persisted values.
+export const MAX_AGENT_TURNS_DEFAULT = 30;
+export const MAX_AGENT_TURNS_MIN = 5;
+export const MAX_AGENT_TURNS_MAX = 500;
+
+export function maxAgentTurnsOutOfRange(value: number | undefined): boolean {
+  return typeof value === "number" && (value < MAX_AGENT_TURNS_MIN || value > MAX_AGENT_TURNS_MAX);
+}
+
+export function normalizeMaxAgentTurns(value: number | undefined): number {
+  const rounded = typeof value === "number" && Number.isFinite(value) ? Math.round(value) : MAX_AGENT_TURNS_DEFAULT;
+  return Math.min(MAX_AGENT_TURNS_MAX, Math.max(MAX_AGENT_TURNS_MIN, rounded));
+}