feat(usage): 添加清理任务与统计过滤

backend/migrations/042_add_usage_cleanup_tasks.sql

@@ -0,0 +1,21 @@
+-- 042_add_usage_cleanup_tasks.sql
+-- 使用记录清理任务表
+
+CREATE TABLE IF NOT EXISTS usage_cleanup_tasks (
+    id BIGSERIAL PRIMARY KEY,
+    status VARCHAR(20) NOT NULL,
+    filters JSONB NOT NULL,
+    created_by BIGINT NOT NULL REFERENCES users(id) ON DELETE RESTRICT,
+    deleted_rows BIGINT NOT NULL DEFAULT 0,
+    error_message TEXT,
+    started_at TIMESTAMPTZ,
+    finished_at TIMESTAMPTZ,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_usage_cleanup_tasks_status_created_at
+    ON usage_cleanup_tasks(status, created_at DESC);
+
+CREATE INDEX IF NOT EXISTS idx_usage_cleanup_tasks_created_at
+    ON usage_cleanup_tasks(created_at DESC);