## Problem
`tea login add` can panic while auto-discovering SSH keys. The interactive login flow calls `regexp.FindStringSubmatch` and immediately indexes `[1]` without checking whether the regex matched. When the selected key display string does not have the expected format, the returned slice is `nil` and tea crashes with:
```
panic: runtime error: index out of range [1] with length 0
```
This is the crash reported in #527.
## Root cause
`regexp.Regexp.FindStringSubmatch` returns `nil` when the input does not match. Indexing that result with `[1]` assumes a match and causes the panic. The same unchecked pattern exists for SSH certificates and plain public keys in `modules/interact/login.go`.
## Changes
- Extract auto-discovered SSH key/certificate display parsing into `parseSSHPubkeySelection`.
- Add a `regexpSubmatch` helper that returns an error when a regex does not match, so login fails with a descriptive error instead of panicking.
- Add table-driven tests for local/agent keys, local/agent certificates, and malformed input.
Fixes#527
---------
Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/1100
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Lunny Xiao