feat(about): show the desktop version and the web build's commit and date (#276)

Settings → About only showed cinny's package version, the same on web
and desktop and unchanged across many deploys a day. vite.config.js now
stamps the short commit (git, or LOTUS_BUILD_COMMIT; "unknown" without
git) and build time into the bundle, and About shows "Web build <commit>
· built <date>", linking the commit. On desktop it also shows "Desktop
<version>" from Tauri's built-in plugin:app|version (allowed by
core:default).

Fixes #276

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/ext.d.ts

@@ -1,5 +1,9 @@
 /// <reference types="vite/client" />
 
+// [Gitea #276] Set by vite.config.js `define`.
+declare const __LOTUS_BUILD_COMMIT__: string;
+declare const __LOTUS_BUILD_DATE__: string;
+
 declare module 'browser-encrypt-attachment' {
   export interface EncryptedAttachmentInfo {
     v: string;