style(www): 更新官网品牌视觉主题

[Yumiue]

背景

官网需要切换到新的 NeoCode 品牌图标，并让整体视觉主题与深蓝黑 + 蜜桃橙的品牌风格保持一致。

当前修改

• 将 VitePress 站点 favicon、导航 logo、Hero 图片和 OG 图片统一切换为新的 PNG 品牌图标。
• 更新首页 Hero、功能卡片、快速开始区块和文档代码块的全局主题样式。
• 删除旧的 SVG 品牌图标，避免继续引用过时资产。

验证

• pnpm docs:build

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[fennoai]

Focused review completed (code quality, performance, security, docs).

I found 3 noteworthy issues: one functional copy-state bug, one lifecycle cleanup issue, and one command-documentation mismatch.

[fennoai]

document.execCommand('copy') returns a boolean and may fail without throwing. In that case this code still reports copy success. Please check the return value and surface failure (e.g., throw when it returns false) so the button state is accurate.

[fennoai]

resetTimer is never cleared on component unmount. If navigation happens before timeout fires, the callback still runs and mutates stale component state. Add onBeforeUnmount(() => clearResetTimer()) to avoid timer leaks and stale updates.

[fennoai]

The docs still advertise --runtime-mode gateway, but CLI help only supports gateway as a subcommand (neocode gateway). This guidance leads to a non-working command (same issue is duplicated again later in this file).