v6.7.3: faster loading, and pages search engines can read

The bundles carried all thirteen translations at once and a page fetched them a
third time as raw source; each page now loads only its own language. Alongside
that: JavaScript is minified, the eight stylesheets are served as one file, the
QR scanner is fetched after the app is up instead of on every visit, Inter ships
once rather than five copies of the same file, and Font Awesome is subset to the
82 icons this app draws instead of all 2468.

1.85 MB across 43 requests becomes under 700 KB across 33. On mobile the page
starts drawing in 1.6 s instead of 6.3 s and is usable in 4.5 s instead of 11 s.

Pages also carry their text in the HTML now. Everything was drawn by JavaScript
into an empty div, so crawlers saw correct metadata around nothing, and twelve of
the thirteen language pages had never been shown to anyone. The documentation is
published under /docs/ with a new FAQ, and unknown addresses return a real 404.

Separately: the localized shells were served with the year-long immutable cache
header meant for static assets, which pinned anyone who opened /de/ or /ru/ to
that build. The header is fixed and the service worker refreshes what it cached.

Claude-Session: https://claude.ai/code/session_014KjzTXxrhzYoDDWChYQ4u2

locales/zh.json

@@ -7,7 +7,6 @@
   "meta": {
     "title": "SecureBit.chat - 私密的端到端加密通讯工具",
     "description": "SecureBit.chat 是一款免费的端到端加密点对点通讯工具，完全在浏览器中运行。无需账号，没有服务器保存你的消息 —— 采用 ECDH P-384、AES-256-GCM 与当面 SAS 校验。",
-    "keywords": "加密通讯, 端到端加密, 点对点聊天, P2P 通讯, ECDH, DTLS, SAS 校验, WebRTC, 私密聊天, 安全聊天, 无服务器, 无需注册, 中间人攻击防护, 前向保密",
     "ogTitle": "SecureBit.chat - 端到端加密的点对点聊天",
     "ogDescription": "完全在浏览器中运行的安全通讯工具。无需账号，没有服务器保存你的消息。可以接入你自己的 STUN/TURN 服务器 —— 我们不做任何强制。",
     "ogImageAlt": "SecureBit.chat - 端到端加密的点对点聊天",