getPod() assumes subdomain pattern, breaks path-based pods

从 src/utils/headerFooterHelpers.ts 中的 getPod() 开始，检查 authn.currentUser()、WebID 数据和 storage 在周边工具函数中是如何可用的。使用类似 http://server.com/alice/ 的基于路径的 pod 验证其行为，并保留现有的、针对子域名 pod 的基于 origin 的 fallback。

Problem

The getPod() function in src/utils/headerFooterHelpers.ts assumes pods are at the origin (subdomain pattern), which breaks path-based pod servers.

Current code (line 17-20):

export function getPod (): NamedNode {
  // @@ TODO: This is given that mashlib runs on NSS - might need to change when we want it to run on other Pod servers
  return sym(document.location.origin).site()
}

The TODO comment acknowledges this limitation.

Impact

When using a path-based pod server (e.g., http://server.com/alice/), after login:

• WebID: http://server.com/alice/profile/card#me ✓
• getPod() returns: http://server.com/ ✗
• Profile guess becomes: http://server.com/profile/card#me ✗
• Should be: http://server.com/alice/profile/card#me ✓

This causes 404 errors when mashlib tries to load the user's profile.

Affected Servers

• Any path-based pod server
• CSS (Community Solid Server) supports both subdomain and path patterns
• JSS (JavaScript Solid Server) uses path pattern

Suggested Fix

Derive the pod root from the logged-in user's WebID rather than assuming document.location.origin:

export function getPod (): NamedNode {
  const user = authn.currentUser()
  if (user) {
    // Extract pod root from WebID's pim:storage or by convention
    const storage = getStorage(user)
    if (storage) return storage
  }
  // Fallback to origin-based (subdomain pattern)
  return sym(document.location.origin).site()
}

Or use the pim:storage triple from the user's profile which explicitly declares the pod root.

Environment

• solid-ui version: latest (via mashlib CDN)
• Server: JSS (JavaScript Solid Server) with path-based pods