docs(CHANGES): Document capture_frame() flag forwarding

why: Document the new capture_frame() parameters for users.

what:
- Add flag forwarding bullet point to capture_frame() feature list

Author: tony

CHANGES

@@ -162,6 +162,8 @@ def test_cli_output(pane, textframe_snapshot):
 - Defaults to pane dimensions when `content_width` / `content_height` not specified
 - Uses `overflow_behavior="truncate"` by default for CI robustness
 - Accepts same `start` / `end` parameters as `capture_pane()`
+- Forwards all `capture_pane()` flags: `escape_sequences`, `escape_non_printable`,
+  `join_wrapped`, `preserve_trailing`, `trim_trailing`
 
 ## libtmux 0.52.1 (2025-12-07)