Reduce turn latency: cap recent events (10→5) + concise-reasoning constraint (v0.9.0)

Fixes #22

server/engine.ts

@@ -59,6 +59,7 @@ export function buildSystemPrompt(preset: Preset): string {
     'HARD CONSTRAINTS',
     '- Use only nation ids and ISO_A3 codes that exist in the provided state.',
     '- Prefer 1-4 events per turn; keep each text 1-3 sentences.',
+    '- Keep your internal reasoning brief (a few sentences) and go straight to the JSON result; do not over-deliberate or re-derive facts already present in the state.',
     '- Keep every stat value between 0 and 100.',
     '- Only change borders when war or a decisive political shift justifies it.',
     '- If a field is not relevant this turn, set it to an empty array.',
@@ -95,7 +96,7 @@ export function buildUserPrompt(state: GameState, items: RoundItem[]): string {
       nations: Object.fromEntries(
         Object.entries(state.nations).map(([id, n]) => [id, nationForPrompt(n)]),
       ),
-      recentEvents: state.events.slice(-10).map((e) => ({
+      recentEvents: state.events.slice(-5).map((e) => ({
         turn: e.turn,
         date: e.date,
         nation: e.nation,