fix: return clean errors and refund quota on AI provider failures

AI routes had no consistent error handling — a provider failure (e.g.
OpenRouter returning a degraded-model error) crashed the route as an
uncaught 500 and, worse, still charged the user's monthly aiCall
quota for a request that never succeeded.

Adds withAiQuota()/aiErrorResponse() (lib/ai/ai-error.ts) and applies
them across all 12 AI generation routes: charges the quota, runs the
AI call, refunds the credit and returns a clean user-facing message
if it throws. Frontend needs no changes — existing dialogs already
toast whatever `error` string comes back.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/app/api/v1/ai/meal-plan/generate/route.ts

@@ -4,6 +4,7 @@ import { db, recipes, recipeIngredients, recipeSteps, mealPlans, mealPlanEntries
 import { requireSession } from "@/lib/api-auth";
 import { applyRateLimit } from "@/lib/rate-limit";
 import { getDefaultProviderWithKey } from "@/lib/ai/resolve-user-key";
+import { aiErrorResponse } from "@/lib/ai/ai-error";
 import { generateMealPlan } from "@/lib/ai/features/generate-meal-plan";
 import { getUserPrivateBio } from "@/lib/ai/user-bio";
 
@@ -52,18 +53,23 @@ export async function POST(req: NextRequest) {
     pantryItemNames = pantry.map((p) => p.rawName);
   }
 
-  const plan = await generateMealPlan(
-    {
-      dietaryPrefs: parsed.data.dietaryPrefs,
-      servings: parsed.data.servings,
-      pantryItems: pantryItemNames,
-      days: parsed.data.days,
-      pantryMode: parsed.data.pantryMode,
-      difficulty: parsed.data.difficulty,
-    },
-    { ...config, userContext: privateBio ?? undefined },
-    locale
-  );
+  let plan;
+  try {
+    plan = await generateMealPlan(
+      {
+        dietaryPrefs: parsed.data.dietaryPrefs,
+        servings: parsed.data.servings,
+        pantryItems: pantryItemNames,
+        days: parsed.data.days,
+        pantryMode: parsed.data.pantryMode,
+        difficulty: parsed.data.difficulty,
+      },
+      { ...config, userContext: privateBio ?? undefined },
+      locale
+    );
+  } catch (err) {
+    return aiErrorResponse(err);
+  }
 
   // Ensure meal plan row exists for the week
   let mealPlan = await db.query.mealPlans.findFirst({