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/key_help.py

@@ -3,7 +3,8 @@ from __future__ import annotations
 
 import curses
 from dataclasses import dataclass
-import unicodedata
+
+from .text import pad_display, truncate_display
 
 
 @dataclass(frozen=True)
@@ -48,36 +49,6 @@ KEY_SECTIONS: tuple[tuple[str, tuple[KeyMapping, ...]], ...] = (
 )
 
 
-def display_width(value: str) -> int:
-    return sum(
-        0
-        if unicodedata.combining(character)
-        else 2
-        if unicodedata.east_asian_width(character) in {"W", "F"}
-        else 1
-        for character in value
-    )
-
-
-def truncate(value: str, width: int) -> str:
-    if width <= 0:
-        return ""
-    result = ""
-    used = 0
-    for character in value:
-        size = display_width(character)
-        if used + size > width:
-            break
-        result += character
-        used += size
-    return result
-
-
-def pad(value: str, width: int) -> str:
-    clipped = truncate(value, width)
-    return clipped + " " * max(0, width - display_width(clipped))
-
-
 class KeyHelpPopup:
     def __init__(self) -> None:
         self.scroll = 0
@@ -95,7 +66,7 @@ class KeyHelpPopup:
                 if wide:
                     lines.append(
                         (
-                            f"  {pad(mapping.keys, key_width)}  {mapping.action}",
+                            f"  {pad_display(mapping.keys, key_width)}  {mapping.action}",
                             curses.A_NORMAL,
                         )
                     )
@@ -172,6 +143,6 @@ class KeyHelpPopup:
         if y < 0 or y >= height or x >= width:
             return
         try:
-            screen.addstr(y, x, truncate(value, max(0, width - x - 1)), attribute)
+            screen.addstr(y, x, truncate_display(value, max(0, width - x - 1)), attribute)
         except curses.error:
             pass