[codex] add account id to feedback uploads (#21498)

## Why

Feedback uploads already carry auth-derived context like
`chatgpt_user_id`, but they do not include the authenticated
workspace/account id. Adding `account_id` makes feedback triage easier
when a user can operate across multiple ChatGPT workspaces.

## What changed

- emit auth-derived `account_id` into feedback tags in `app-server`
before the feedback snapshot is uploaded
- preserve that tag through `codex-feedback` upload tag assembly
alongside the existing merge behavior for other tags
- extend `codex-feedback` coverage to assert that snapshot-derived
`account_id` is present in uploaded tags

## Verification

- `cargo test -p codex-feedback
upload_tags_include_client_tags_and_preserve_reserved_fields`
- `cargo test -p codex-app-server --lib feedback_processor`

codex-rs/feedback/src/lib.rs

@@ -757,6 +757,7 @@ mod tests {
         tags.insert("cli_version".to_string(), "wrong-version".to_string());
         tags.insert("session_source".to_string(), "wrong-source".to_string());
         tags.insert("reason".to_string(), "wrong-reason".to_string());
+        tags.insert("account_id".to_string(), "actual-account".to_string());
         tags.insert("model".to_string(), "gpt-5".to_string());
         let snapshot = FeedbackSnapshot {
             bytes: Vec::new(),
@@ -809,6 +810,10 @@ mod tests {
             upload_tags.get("reason").map(String::as_str),
             Some("actual reason")
         );
+        assert_eq!(
+            upload_tags.get("account_id").map(String::as_str),
+            Some("actual-account")
+        );
         assert_eq!(
             upload_tags.get("client_tag").map(String::as_str),
             Some("from-client")