feat(tui): route employee feedback follow-ups to internal link (#10198)

## Problem
OpenAI employees were sent to the public GitHub issue flow after
`/feedback`, which is the wrong follow-up path internally.

## Mental model
After feedback upload completes, we render a follow-up link/message.
That link should be audience-aware but must not change the upload
pipeline itself.

## Non-goals
- Changing how feedback is captured or uploaded
- Changing external user behavior

## Tradeoffs
We detect employees via the authenticated account email suffix
(`@openai.com`). If the email is unavailable (e.g., API key auth), we
default to the external behavior.

## Architecture
- Introduce `FeedbackAudience` and thread it from `App` -> `ChatWidget`
-> `FeedbackNoteView`
- Gate internal messaging/links on `FeedbackAudience::OpenAiEmployee`
- Internal follow-up link is now `http://go/codex-feedback-internal`
- External GitHub URL remains byte-for-byte identical

## Observability
No new telemetry; this only changes rendered follow-up instructions.

## Tests
- `just fmt`
- `cargo test -p codex-tui --lib`

codex-rs/tui/src/bottom_pane/mod.rs

@@ -67,6 +67,7 @@ mod slash_commands;
 pub(crate) use footer::CollaborationModeIndicator;
 pub(crate) use list_selection_view::SelectionViewParams;
 mod feedback_view;
+pub(crate) use feedback_view::FeedbackAudience;
 pub(crate) use feedback_view::feedback_disabled_params;
 pub(crate) use feedback_view::feedback_selection_params;
 pub(crate) use feedback_view::feedback_upload_consent_params;