Agent jobs (spawn_agents_on_csv) + progress UI (#10935)

## Summary
- Add agent job support: spawn a batch of sub-agents from CSV, auto-run,
auto-export, and store results in SQLite.
- Simplify workflow: remove run/resume/get-status/export tools; spawn is
deterministic and completes in one call.
- Improve exec UX: stable, single-line progress bar with ETA; suppress
sub-agent chatter in exec.

## Why
Enables map-reduce style workflows over arbitrarily large repos using
the existing Codex orchestrator. This addresses review feedback about
overly complex job controls and non-deterministic monitoring.

## Demo (progress bar)
```
./codex-rs/target/debug/codex exec \
  --enable collab \
  --enable sqlite \
  --full-auto \
  --progress-cursor \
  -c agents.max_threads=16 \
  -C /Users/daveaitel/code/codex \
  - <<'PROMPT'
Create /tmp/agent_job_progress_demo.csv with columns: path,area and 30 rows:
path = item-01..item-30, area = test.

Then call spawn_agents_on_csv with:
- csv_path: /tmp/agent_job_progress_demo.csv
- instruction: "Run `python - <<'PY'` to sleep a random 0.3–1.2s, then output JSON with keys: path, score (int). Set score = 1."
- output_csv_path: /tmp/agent_job_progress_demo_out.csv
PROMPT
```

## Review feedback addressed
- Auto-start jobs on spawn; removed run/resume/status/export tools.
- Auto-export on success.
- More descriptive tool spec + clearer prompts.
- Avoid deadlocks on spawn failure; pending/running handled safely.
- Progress bar no longer scrolls; stable single-line redraw.

## Tests
- `cd codex-rs && cargo test -p codex-exec`
- `cd codex-rs && cargo build -p codex-cli`

codex-rs/core/tests/suite/shell_snapshot.rs

@@ -52,10 +52,16 @@ async fn wait_for_snapshot(codex_home: &Path) -> Result<PathBuf> {
     let snapshot_dir = codex_home.join("shell_snapshots");
     let deadline = Instant::now() + Duration::from_secs(5);
     loop {
-        if let Ok(mut entries) = fs::read_dir(&snapshot_dir).await
-            && let Some(entry) = entries.next_entry().await?
-        {
-            return Ok(entry.path());
+        if let Ok(mut entries) = fs::read_dir(&snapshot_dir).await {
+            while let Some(entry) = entries.next_entry().await? {
+                let path = entry.path();
+                let Some(extension) = path.extension().and_then(|ext| ext.to_str()) else {
+                    continue;
+                };
+                if extension == "sh" || extension == "ps1" {
+                    return Ok(path);
+                }
+            }
         }
 
         if Instant::now() >= deadline {