tui: fix approval dialog for large commands (#3087)

#### Summary
- Emit a “Proposed Command” history cell when an ExecApprovalRequest
arrives (parity with proposed patches).
- Simplify the approval dialog: show only the reason/instructions; move
the command preview into history.
- Make approval/abort decision history concise:
  - Single line snippet; if multiline, show first line + " ...".
  - Truncate to 80 graphemes with ellipsis for very long commands.

#### Details
- History
- Add `new_proposed_command` to render a header and indented command
preview.
  - Use shared `prefix_lines` helper for first/subsequent line prefixes.
- Approval UI
- `UserApprovalWidget` no longer renders the command in the modal; shows
optional `reason` text only.
  - Decision history renders an inline, dimmed snippet per rules above.
- Tests (snapshot-based)
  - Proposed/decision flow for short command.
  - Proposed multi-line + aborted decision snippet with “ ...”.
  - Very long one-line command -> truncated snippet with “…”.
  - Updated existing exec approval snapshots and test reasons.

<img width="1053" height="704" alt="Screenshot 2025-09-03 at 11 57
35 AM"
src="https://github.com/user-attachments/assets/9ed4c316-9daf-4ac1-80ff-7ae1f481dd10"
/>

after approving:

<img width="1053" height="704" alt="Screenshot 2025-09-03 at 11 58
18 AM"
src="https://github.com/user-attachments/assets/a44e243f-eb9d-42ea-87f4-171b3fb481e7"
/>

rejection:

<img width="1053" height="207" alt="Screenshot 2025-09-03 at 11 58
45 AM"
src="https://github.com/user-attachments/assets/a022664b-ae0e-4b70-a388-509208707934"
/>

big command:


https://github.com/user-attachments/assets/2dd976e5-799f-4af7-9682-a046e66cc494

codex-rs/tui/src/render/line_utils.rs

@@ -34,3 +34,26 @@ pub fn is_blank_line_spaces_only(line: &Line<'_>) -> bool {
         .iter()
         .all(|s| s.content.is_empty() || s.content.chars().all(|c| c == ' '))
 }
+
+/// Prefix each line with `initial_prefix` for the first line and
+/// `subsequent_prefix` for following lines. Returns a new Vec of owned lines.
+pub fn prefix_lines(
+    lines: Vec<Line<'static>>,
+    initial_prefix: Span<'static>,
+    subsequent_prefix: Span<'static>,
+) -> Vec<Line<'static>> {
+    lines
+        .into_iter()
+        .enumerate()
+        .map(|(i, l)| {
+            let mut spans = Vec::with_capacity(l.spans.len() + 1);
+            spans.push(if i == 0 {
+                initial_prefix.clone()
+            } else {
+                subsequent_prefix.clone()
+            });
+            spans.extend(l.spans);
+            Line::from(spans)
+        })
+        .collect()
+}