feat(table): add --border-row to draw a separator between every row

[WladmirJunior]

What

Exposes two lipgloss/table capabilities that the table command did not surface:

• --border-row (env GUM_TABLE_BORDER_ROW) — draw a horizontal separator
  between every data row, not just after the header.
• --width (env GUM_TABLE_WIDTH) — set a fixed total table width; columns
  auto-size to fit. 0 (default) keeps the current content-based sizing.

Both are opt-in; defaults are unchanged, so no behavior change for existing users.

Why

lipgloss/table already supports BorderRow(true) and Width(w); gum table
just did not expose them. Per-row dividers match what SQL CLIs (grid mode),
tabulate (grid) and tty-table do by default, and a fixed width lets a table
line up with surrounding UI (e.g. a header box of the same width).

Before / After

printf "Machine type|Personal Mac
AI agent CLIs|claude, codex
" | \
  gum table -p --separator="|" --border double --columns "Component,Selection"

Before (content-sized, divider only after the header):

╔══════════════╦══════════════╗
║ Component    ║ Selection    ║
╠══════════════╬══════════════╣
║ Machine type ║ Personal Mac ║
║ AI agent CLIs║ claude, codex║
╚══════════════╩══════════════╝

After (--border-row --width 72):

╔═══════════════════════════════════╦══════════════════════════════════╗
║ Component                         ║ Selection                        ║
╠═══════════════════════════════════╬══════════════════════════════════╣
║ Machine type                      ║ Personal Mac                     ║
╠═══════════════════════════════════╬══════════════════════════════════╣
║ AI agent CLIs                     ║ claude, codex                    ║
╚═══════════════════════════════════╩══════════════════════════════════╝