fix: stop terminal scrolling to top on tool execution (#248)

* fix: detect terminal width via stderr when stdout is piped

When Claude Code runs the statusLine as a subprocess, stdout is captured
(piped), so process.stdout.columns is undefined. With no terminal width,
long lines aren't wrapped by the HUD — the terminal wraps them silently
instead. Claude Code counts \n characters to determine how many lines to
erase on the next render, so the physical line count diverges from what
Claude Code expects. Over successive renders the cursor drifts upward into
the scrollback buffer, causing the terminal to jump to the top on every
tool execution (#209).

Fix: fall back to process.stderr.columns before the COLUMNS env var.
When the statusLine subprocess is spawned, only stdout is redirected;
stderr remains connected to the real TTY and returns the correct width.
With accurate width, lines are properly wrapped in the HUD output and
Claude Code's line count stays consistent.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore: drop dist artifacts and cover stderr width

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Jarrod Watts <jarrod@cubelabs.xyz>

Author: 3 people