chore(modell): rikta ALLT mot gemini-3.1-flash-lite + fixa kostnadsberakning

Koden/docs pastod overallt gemini-3.5-flash-lite fast .env kor 3.1. Nu enhetligt
3.1 i .env.example, config.ts-default, gemini.ts-default, tester, eval och docs
(09 + 10). Dessutom en RIKTIG bugg: estimateCostUsd rakna pa 3.5-priser
($0,30/$2,50) medan vi kor 3.1 -> overskattade spend och troffade budgetlarmet
for tidigt. Nu 3.1-priser ($0,25/$1,50). docs/10 helt omraknad pa 3.1 (per
uppgift, per anvandare, skala, 100k-trial-scenariot). Referenslinje kvar som
visar 3.5-priset for att motivera valet.

packages/ai-contracts/src/gemini.ts

@@ -313,7 +313,7 @@ export class GeminiAamosClient implements AamosClient {
   constructor(config: GeminiAamosClientConfig) {
     this.cfg = {
       apiKey: config.apiKey,
-      model: config.model ?? "gemini-3.5-flash-lite",
+      model: config.model ?? "gemini-3.1-flash-lite",
       timeoutMs: config.timeoutMs ?? 60_000,
       dailyBudgetUsd: config.dailyBudgetUsd ?? 0,
       promptVersion: config.promptVersion ?? "gemini-fridge-v4",
@@ -1069,8 +1069,9 @@ Språk: ${lang}.`;
   }
 
   private estimateCostUsd(inputTokens: number, outputTokens: number): number {
-    // Gemini 3.5 Flash Lite standard-tier pricing (2026): $0.30/1M input, $2.50/1M output.
-    return inputTokens * 0.3e-6 + outputTokens * 2.5e-6;
+    // Gemini 3.1 Flash Lite standard-tier pricing (2026): $0.25/1M input, $1.50/1M output.
+    // (Matcha GEMINI_MODEL i .env / config.ts – kör vi 3.1, ska kostnaden räknas på 3.1.)
+    return inputTokens * 0.25e-6 + outputTokens * 1.5e-6;
   }
 
   private async isOverBudget(estimateUsd: number): Promise<boolean> {

packages/ai-contracts/test/gemini.test.ts

@@ -67,7 +67,7 @@ describe("GeminiAamosClient", () => {
     const budget = new MemoryBudgetStore();
     const client = new GeminiAamosClient({
       apiKey: "test-key",
-      model: "gemini-3.5-flash-lite",
+      model: "gemini-3.1-flash-lite",
       fetchImpl: makeFetch(JPEG_BYTES),
       budgetStore: budget,
       dailyBudgetUsd: 10,
@@ -82,7 +82,7 @@ describe("GeminiAamosClient", () => {
 
     expect(result.status).toBe("ok");
     expect(result.output).not.toBeNull();
-    expect(result.modelVersion).toBe("gemini-3.5-flash-lite");
+    expect(result.modelVersion).toBe("gemini-3.1-flash-lite");
     expect(result.costUsd).toBeGreaterThan(0);
     expect(result.inputTokens).toBe(392);
     expect(result.outputTokens).toBe(121);