Refactor VSR web: align UI with df-autotest, add auth and platform worker

- Redesign web/index.html to match df-autotest light theme (sidebar layout,
  same token system, badges, panels, modals, toast notifications)
- Add simple cookie-based auth (ADMIN_PASSWORD env via .env)
- Add platform Worker (poll external platform for VSR tasks, sign requests
  with HMAC same as df-autotest)
- Add Settings page for platform connection config (DB-stored, no env vars)
- Add worker log API with incremental polling
- Remove bottom console strip; add per-task log modal with SQLite persistence
- Task table: add created_at / started_at columns, move progress to detail modal
- Fix modal close buttons (direct onclick, remove unreliable data-close delegation)
- Load .env via python-dotenv on startup

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,13 @@
+# VSR Web 配置示例 — 复制为 .env 后修改
+# 参考 df-autotest-platform 的 .env 结构
+
+# 管理员密码（留空则不需要登录）
+ADMIN_PASSWORD=
+
+# 存储目录（默认 ./web_cache）
+# VSR_STORAGE=./web_cache
+
+# 服务监听端口（默认 8001）
+# PORT=8001
+
+# Platform Worker 连接信息在「系统设置」页面配置，无需在此设置

.gitignore

@@ -376,3 +376,4 @@ test*_no_sub*.mp4
 inference.onnx
 /config/config.json
 web_cache/
+.env