feat: initial commit - oncology literature search platform

OncoLit: a multi-tenant oncology literature search, feed, and
collaboration platform. Built with FastAPI + Vue 3 + PostgreSQL.
Includes PubMed pipeline, drug approvals, AI summaries, and
systematic review tools.

frontend/src/composables/useGlobalLoading.ts

@@ -0,0 +1,30 @@
+/** 全局请求加载状态 — 由 axios 拦截器自动维护 */
+import { ref, watch } from 'vue'
+
+/** 当前在途请求数 */
+const pendingCount = ref(0)
+
+/** 是否显示加载条（延迟 300ms 后为 true，避免闪烁） */
+const showBar = ref(false)
+
+let timer: ReturnType<typeof setTimeout> | null = null
+
+watch(pendingCount, (count) => {
+  if (count > 0) {
+    // 请求开始后 300ms 才显示（快请求不闪条）
+    if (timer === null) {
+      timer = setTimeout(() => { showBar.value = true }, 300)
+    }
+  } else {
+    // 所有请求完成 → 立即隐藏
+    showBar.value = false
+    if (timer !== null) { clearTimeout(timer); timer = null }
+  }
+})
+
+export function useGlobalLoading() {
+  function increment() { pendingCount.value++ }
+  function decrement() { if (pendingCount.value > 0) pendingCount.value-- }
+
+  return { pendingCount, showBar, increment, decrement }
+}