fix(tui): increase paste burst char interval on Windows to 30ms (#9348)

## Summary

- Increases `PASTE_BURST_CHAR_INTERVAL` from 8ms to 30ms on Windows to
fix multi-line paste issues in VS Code integrated terminal
- Follows existing pattern of platform-specific timing (like
`PASTE_BURST_ACTIVE_IDLE_TIMEOUT`)

## Problem

When pasting multi-line text in Codex CLI on Windows (especially VS Code
integrated terminal), only the first portion is captured before
auto-submit. The rest arrives as a separate message.

**Root cause**: VS Code's terminal emulation adds latency (~10-15ms per
character) between key events. The 8ms `PASTE_BURST_CHAR_INTERVAL`
threshold is too tight - characters arrive slower than expected, so
burst detection fails and Enter submits instead of inserting a newline.

## Solution

Use Windows-specific timing (30ms) for `PASTE_BURST_CHAR_INTERVAL`,
following the same pattern already used for
`PASTE_BURST_ACTIVE_IDLE_TIMEOUT` (60ms on Windows vs 8ms on Unix).

30ms is still fast enough to distinguish paste from typing (humans type
~200ms between keystrokes).

## Test plan

- [x] All existing paste_burst tests pass
- [ ] Test multi-line paste in VS Code integrated PowerShell on Windows
- [ ] Test multi-line paste in standalone Windows PowerShell
- [ ] Verify no regression on macOS/Linux

Fixes #2137

Co-authored-by: Josh McKinney <joshka@openai.com>

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

@@ -151,10 +151,18 @@ use std::time::Instant;
 // Heuristic thresholds for detecting paste-like input bursts.
 // Detect quickly to avoid showing typed prefix before paste is recognized
 const PASTE_BURST_MIN_CHARS: u16 = 3;
-const PASTE_BURST_CHAR_INTERVAL: Duration = Duration::from_millis(8);
 const PASTE_ENTER_SUPPRESS_WINDOW: Duration = Duration::from_millis(120);
-// Slower paste burts have been observed in windows environments, but ideally
-// we want to keep this low
+
+// Maximum delay between consecutive chars to be considered part of a paste burst.
+// Windows terminals (especially VS Code integrated terminal) deliver paste events
+// more slowly than native terminals, so we use a higher threshold there.
+#[cfg(not(windows))]
+const PASTE_BURST_CHAR_INTERVAL: Duration = Duration::from_millis(8);
+#[cfg(windows)]
+const PASTE_BURST_CHAR_INTERVAL: Duration = Duration::from_millis(30);
+
+// Idle timeout before flushing buffered paste content.
+// Slower paste bursts have been observed in Windows environments.
 #[cfg(not(windows))]
 const PASTE_BURST_ACTIVE_IDLE_TIMEOUT: Duration = Duration::from_millis(8);
 #[cfg(windows)]