[FEATURE] Show actionable error message when GitHub repo indexing fails in Projects

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When a GitHub repository added to a Claude.ai Project fails to index — for example due to insufficient GitHub App permissions — the UI provides no error feedback whatsoever. The project files panel shows the repository tile with a progress bar stuck at 0% and a perpetual "Indexing" indicator, with no timeout, no error message, and no guidance on what to do.
In my case, the indexing indicator remained stuck for over 24 hours. Manually uploaded markdown files in the same project indexed within seconds, confirming the issue was specific to the GitHub repository connection. The root cause turned out to be that the Claude GitHub App did not have the correct permissions on the repository. Once I updated the permissions on the GitHub side, the repository indexed successfully.
The problem is that there was zero indication that permissions were the issue. The UI gave no signal that anything was wrong — it simply showed an indefinitely stuck progress indicator. Finding the solution required external research and trial-and-error.

Proposed Solution

Feature Description

If the GitHub connector fails to retrieve repository data (e.g. due to insufficient permissions, access errors, or other issues), display an actionable error message to the user instead of silently stopping the synchronization and leaving the progress indicator stuck indefinitely.
Note: A "Sync now" button already exists which can serve as a retry mechanism — the issue is purely that the user has no idea why indexing failed or what to fix before retrying.

Why This Matters
This is a recurring pain point. Multiple existing bug reports describe the same symptom pattern — repos that appear connected but silently fail to index:

#10647 — GitHub sync broken, connector shows "Connected" but files not accessible
#12839 — Private repos fail to sync after GitHub App reinstall
#17807 — Subdirectories not loading (blank file browser)
#17824 — GitHub integration showing 0% capacity for all files
#27155 — GitHub repos not visible despite app installed
#1884 — Sync loads forever and does not complete

In all of these cases, the user experience is the same: something is broken, but the UI gives no indication of what or why. Users are left guessing, filing bug reports, or abandoning the feature.
A clear error message with a link to the relevant GitHub settings page would have immediately resolved my issue and likely many of the above reports.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

File operations

Use Case Example

_No response_

Additional Context

Environment

Platform: Claude Desktop (Projects)
This is a Claude Desktop feature request, not Claude Code CLI or claude.ai web