make repo error messages actionable (#550, #379, #519)

Rewrite repo_access_limited, repo_not_found, repo_empty, and
repo_not_accessible to point users at concrete next steps instead
of stating only that something failed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: tdurieux

public/i18n/locale-en.json

@@ -8,10 +8,10 @@
     "not_authorized": "You do not have permission to perform this action.",
     "unable_to_connect_user": "Unable to connect your account. Please try again later.",
     "user_not_found": "The requested user could not be found.",
-    "repo_access_limited": "Access to repository limited by org.",
-    "repo_not_found": "The repository is not found.",
-    "repo_empty": "The source repository is empty on GitHub.",
-    "repo_not_accessible": "Anonymous GitHub is unable to or is forbidden to access the repository.",
+    "repo_access_limited": "GitHub blocked access because the repository's organization restricts third-party OAuth apps. Ask an org owner to approve Anonymous GitHub under Settings → Third-party Access → OAuth app policy, or anonymize a personal fork instead.",
+    "repo_not_found": "The repository was not found on GitHub. Check the URL and spelling, make sure you are signed in to the account that can see it, and confirm the repo isn't hidden under an org that restricts third-party app access.",
+    "repo_empty": "The selected branch has no commits on GitHub. Push at least one commit, or pick a different branch, then retry.",
+    "repo_not_accessible": "Anonymous GitHub cannot access this repository. Verify the repository exists and that Anonymous GitHub has been authorized for the owning organization.",
     "repository_expired": "The repository is expired.",
     "repository_not_ready": "Anonymous GitHub is still processing the repository, it can take several minutes.",
     "repository_not_accessible": "This repository is currently not accessible.",