fix(收藏/聊天记录检索): 切换页内tab不再污染浏览器历史记录

用户反馈"我的收藏"页面点击tabs切换(全部/图片/视频/文件/语音/文本/链接)会记录到浏览器
历史记录里，导致点击返回一直在这个页面内切换tab，而不是真正返回上一页。

根因：content-library-view.jsx的Favorites/HistoryNav每次切tab都调用navigate()，
即HashNavigation.navigateTo() -> location.hash = ...，每次赋值都会被浏览器记为一条
新的历史记录。切N次tab就push N条记录，无论是系统返回键还是应用自己的"返回"按钮
(HashNavigation.goBack())，都要先把这N条tab切换记录走完才能真正离开页面。

修复：新增HashNavigation.navigateReplace()，用history.replaceState替换当前历史记录
而不是新增一条（hash该更新还是更新，刷新/复制链接不受影响），并手动派发hashchange事件
供tinode-web.jsx现有的监听器捕获——replaceState本身不会自动触发该事件。Favorites的
TYPE_LABELS tabs和HistoryNav（"查找聊天记录"页的聊天记录/图片/视频/文件/链接tabs）
两处tab切换都改用这个新方法，不再计入navigationCount。

已在浏览器实测两处：连续切3次tab后，无论是原生history.back()还是应用返回按钮，都能
一次性返回到进入这个页面之前的真实上一页，不再卡在tab切换历史里。

src/lib/navigation.js

@@ -40,6 +40,22 @@ export default class HashNavigation {
     window.location.hash = url;
   }
 
+  // For switching between sub-tabs of the *same* page (e.g. content-library-view.jsx's favorites/
+  // history type tabs), not for navigating to a different page. `navigateTo`/`location.hash =`
+  // always pushes a new history entry, so clicking through N tabs pushes N entries -- the system
+  // back button (and this class's own goBack()) then has to step back through every tab the user
+  // ever visited before it reaches whatever page they were actually on before this one. `replaceState`
+  // updates the hash (still correct for a refresh or a copied link) without adding a history entry,
+  // so it doesn't inflate navigationCount either -- a tab switch was never a real in-app navigation
+  // to begin with. replaceState doesn't fire `hashchange` on its own, so dispatch one manually for
+  // the existing `window.addEventListener('hashchange', ...)` listener (tinode-web.jsx's
+  // handleHashRoute) to pick up; that handler re-reads window.location.hash itself rather than the
+  // event, so a synthetic event with no detail is indistinguishable from a real one to it.
+  static navigateReplace(url) {
+    window.history.replaceState(null, '', '#' + url);
+    window.dispatchEvent(new Event('hashchange'));
+  }
+
   // Real "back": retraces the hash the user was actually on before, via native browser history,
   // rather than a page's own guess at where it must have been reached from. Returns whether it
   // actually did that -- every call site already has its own hardcoded-destination `navigate(...)`