feat: add provider analytics summary

backend/app/schemas/story_schemas.py

@@ -222,6 +222,19 @@ class GenerationProviderStatsResponse(BaseModel):
     by_provider: list[GenerationProviderStatResponse] = Field(default_factory=list)
 
 
+class GenerationProviderAnalyticsResponse(BaseModel):
+    """Provider call stats aggregated across one user's generation history."""
+
+    total_calls: int
+    successful_calls: int
+    failed_calls: int
+    avg_latency_ms: float | None = None
+    estimated_cost_usd: float = 0.0
+    job_count: int
+    story_count: int
+    by_provider: list[GenerationProviderStatResponse] = Field(default_factory=list)
+
+
 class AchievementItem(BaseModel):
     """Achievement item returned for a story."""