feat(ai): AnalysisService 核心编排 + PromptService + UsageService

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/erp-ai/src/service/usage.rs

@@ -0,0 +1,45 @@
+use sea_orm::ActiveModelTrait;
+use sea_orm::Set;
+use uuid::Uuid;
+
+use crate::entity::ai_usage;
+use crate::error::AiResult;
+
+pub struct UsageService {
+    pub db: sea_orm::DatabaseConnection,
+}
+
+impl UsageService {
+    pub fn new(db: sea_orm::DatabaseConnection) -> Self {
+        Self { db }
+    }
+
+    pub async fn log_usage(
+        &self,
+        tenant_id: Uuid,
+        provider: &str,
+        model: &str,
+        analysis_type: &str,
+        input_tokens: u32,
+        output_tokens: u32,
+        duration_ms: u64,
+        cost_cents: i32,
+        is_cache_hit: bool,
+    ) -> AiResult<ai_usage::Model> {
+        let id = Uuid::now_v7();
+        let active = ai_usage::ActiveModel {
+            id: Set(id),
+            tenant_id: Set(tenant_id),
+            provider: Set(provider.into()),
+            model: Set(model.into()),
+            analysis_type: Set(analysis_type.into()),
+            input_tokens: Set(input_tokens as i32),
+            output_tokens: Set(output_tokens as i32),
+            duration_ms: Set(duration_ms as i32),
+            cost_cents: Set(cost_cents),
+            is_cache_hit: Set(is_cache_hit),
+            created_at: Set(chrono::Utc::now()),
+        };
+        Ok(active.insert(&self.db).await?)
+    }
+}