Update VESTS APR label to 'HP (VESTS) APR' in chain info display

Changes:
- Updated HP_VEST_APR_LABEL constant from "HP/VESTS APR" to "HP (VESTS) APR"
  with space before parentheses in data_labels.py
- Added HP_VEST_APR_LABEL import in show_chain.py for consistency
- Replaced hardcoded "VESTS APR" string with HP_VEST_APR_LABEL constant
- Updated docstring example in humanize.py to reflect new format

This change improves clarity and maintains consistency with TUI display
and other label constants used throughout the codebase.

Closes #515

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>