Unify terminal display-width helpers

key_help, selector and control each carried their own East Asian width
and truncation logic with slightly different rules, and cli clipped tmux
labels by code point, so a CJK display name ran twice as wide as an
ASCII one before its ellipsis appeared.

Move the cell-width helpers into herdr_hub.text, make truncate_label
cell-aware, and sanitise control characters before curses draws a row
so an escape sequence in a remote error cannot be rendered as ^[ and
misalign the list.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

herdr_hub/cli.py

@@ -44,6 +44,7 @@ from .selector import (
     SessionSelector,
     StopSessionOutcome,
 )
+from .text import display_width, truncate_display
 
 
 DEFAULT_SOCKET_NAME = "herdr-hub"
@@ -199,13 +200,18 @@ def validate_remote_target(target: str | None) -> None:
 
 
 def truncate_label(label: str, limit: int = 48) -> str:
+    """Clip a tmux window label to ``limit`` terminal cells.
+
+    tmux renders names by cell, so clipping by code point let CJK names run
+    twice as wide as ASCII ones before the ellipsis appeared.
+    """
     clean = "".join(
         character if ord(character) >= 32 and ord(character) != 127 else "?"
         for character in label
     )
-    if len(clean) <= limit:
+    if display_width(clean) <= limit:
         return clean
-    return clean[: limit - 1] + "…"
+    return truncate_display(clean, limit - 1) + "…"
 
 
 def display_target(target: str) -> str: