Chat: the day divider is a section heading, so it dresses like one

A transcript's ``── Wed Aug 12 ──`` does exactly what a grouped list's
heading does — it pins to the top row while its day scrolls under it, and
^PgUp/^PgDn step by it — but it was drawn muted, which reads as chrome and
put the one landmark in the scrollback below the messages it labels. It
takes the accent every other section heading in the app wears.

The rule above the compose line keeps its grey: that one really is chrome.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

meshterm/ui/chat.py

@@ -392,8 +392,13 @@ class ChatScreen(Screen):
                 if new_day:
                     if lines:
                         lines += render_lines(Text(""), width)
+                    # A day divider is this transcript's section heading — it pins to the
+                    # top row while its day scrolls under it and ^PgUp/^PgDn step by it —
+                    # so it wears the app's heading dress (``── Label ──`` in accent, see
+                    # menus.section_heading) rather than reading as grey chrome. The rule
+                    # above the compose line stays muted: that one really is chrome.
                     divider = render_lines(
-                        Text(f"── {stamp:%a} {stamp:%b} {stamp.day} ──", style="muted"), width
+                        Text(f"── {stamp:%a} {stamp:%b} {stamp.day} ──", style="accent"), width
                     )
                     self._sticky_headers.append((len(lines), [divider[0]]))
                     lines += divider