fix: ux inconsistency

[SAHU-01]

Title

This PR fixes two related UX issues with 504 error page:

1. Issue Error handling UX inconsistency #817: Error pages disappear on refresh, showing homepage instead
2. Issue Bubble up errors better #816: Generic 504 errors don't explain the underlying cause

Description

Issue #817: Error Page Inconsistency on Refresh

When users encounter an error (like a 504 timeout), the error page displays correctly initially. However, refreshing the page causes the URL to stay the same while the content changes. This creates confusion as the URL and content are inconsistent.

Cause: The service worker was fetching error page HTML from an external file (/ipfs-sw-504.html). On refresh, this fetch could fail, causing the service worker to fall back to serving the homepage.

Issue #816: Lack of Specific Error Information

When errors occur (hash verification failures, missing providers, network issues), users only see a generic "504 Gateway Timeout" message. The console shows detailed error information, but users aren't informed about what specifically went wrong.

Cause: All errors were being returned with generic messaging, without parsing or surfacing the specific error details to the user.

Notes & open questions

The solution now detects and provides specific information for:

• Hash verification failures (502 Bad Gateway)
• No providers found (504 Gateway Timeout)
• Network errors (503 Service Unavailable)
• Generic timeouts (504 Gateway Timeout)
• Invalid CIDs (400 Bad Request)

Screenshots

For 817:

Before

before.1.mp4

After:

after.1.1.1.mp4

For 816:

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works

[hsanjuan]

Triage:

• @achingbrain will check after merging the error pages stuff as it will cause conflicts probably