refactor: drop the URL-based error classifier and hint lookups

Errors are named by the service call that failed: Classify,
NotFoundError and ConflictError at the call site. Remove the endpoint
parser that guessed the resource from the request path, and the
follow-up reads the explainer made at error time (repository state,
issue-vs-pull-request, the existing pull request's URL) together with
the credentialed transport each API error carried for them.

Calls that the endpoint parser covered and the services did not now
classify themselves: issues, pull requests, reviews, comments,
releases, branches, wiki pages, repositories, organizations and SSH
keys. Unclassified failures fall back to the generic
"not found (HTTP 404 GET ...)" text.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/issues.go

@@ -512,7 +512,7 @@ func itemError(err error, scope string) error {
 	if apiErr, ok := errors.AsType[*transport.APIError](err); ok && apiErr.Status == http.StatusNotFound {
 		return explain(err, "not found in %s", scope)
 	}
-	return services.ClassifyRequest(err)
+	return err
 }
 
 // nameFilter splits a comma-separated filter of kind, trimming entries and rejecting blanks.