feat(renderer): add left/right option for Default Padding

[vishnujayvel]

Closes #482, requested by @riptscripts.

Summary

The Default Padding setting always applied to both the left and
right of each widget. This adds a defaultPaddingSide setting
(both / left / right) so padding can be narrowed to one side.

• Both (left + right) — current behavior, still the default
• Left only
• Right only

Existing configs are unaffected — defaultPaddingSide defaults to
'both', so nothing changes unless you opt in.

Where it's applied

• Standard (non-Powerline) rendering — renderStatusLine in
  src/utils/renderer.ts
• Powerline rendering — renderPowerlineStatusLine in the same file
• Alignment width accounting — calculateMaxWidthsFromPreRendered
  now counts only the side(s) actually applied, so Powerline
  auto-align columns stay correct when padding is one-sided

merge: 'no-padding' interactions are preserved: a side that's
already suppressed by a no-padding merge stays suppressed regardless
of the padding-side setting. Covered by regression tests in both
renderers (see Testing below).

UI

Exposed in the Global Overrides menu (src/tui/components/GlobalOverridesMenu.tsx),
next to Default Padding:

  Default Padding: " "  - Press (p) to edit
     Padding Side: Both  - Press (d) to cycle

Press (d) to cycle Both → Left only → Right only → Both. Available
in both standard and Powerline modes, matching how Default Padding
itself is already exposed in both modes.

Docs

Updated docs/USAGE.md (Default Padding & Separators section) to
describe the new option and keybinding.

Testing

bun run lint              # bun tsc --noEmit && eslint . --max-warnings=0 — clean
bun test                  # full suite green once known-flaky Ink timing tests settle

Added src/utils/__tests__/renderer-padding-side.test.ts covering:

• default (both) behavior is unchanged
• left/right in standard rendering
• left/right in Powerline rendering
• calculateMaxWidthsFromPreRendered width accounting for each side
• merge: 'no-padding' takes precedence over the padding-side setting
  (no double-pad, correct glue) in both standard and Powerline mode,
  for both left and right

All assertions strip SGR codes before comparing (stripSgrCodes from
src/utils/ansi.ts), per repo convention (see renderer-flex-width.test.ts; the
separator-collapse tests strip SGR inline the same way) — chalk.reset() reacts to ambient
color-support (FORCE_COLOR/NO_COLOR), independent of the colorLevel
set on Settings, so an unstripped exact-string assertion would be
environment-dependent. Verified the new file passing under both
FORCE_COLOR=1 and NO_COLOR=1.

Added a GlobalOverridesMenu.test.ts case for the new (d) keybinding
(cycles both → left → right → both), mirroring the existing (m)
minimalist-mode toggle test pattern.

Also updated two pre-existing widget tests
(CurrentWorkingDir.test.ts, CustomCommand.test.ts) that construct
a full Settings object literal rather than spreading
DEFAULT_SETTINGS — they needed the new required field added, same
as any other defaulted Settings field.

Full-suite runs are noisy independent of this change: a handful of
Ink stdin-timing tests (e.g. PowerlineThemeSelector, InstallMenu,
occasionally a GlobalOverridesMenu gradient-selector case,
fetchUsageData's error-handling timer case) flake under full-suite
parallel load but pass individually. Confirmed by running the full
suite twice on a clean, unmodified main checkout (via git stash) —
different tests flaked each time, none of them touching padding or
Settings. Every test file this PR touches passes consistently in
isolation.

Notes

No CURRENT_VERSION/migration bump needed — defaultPaddingSide is
a new field with a Zod .default('both'), the same pattern used for
gitCacheTtlSeconds, minimalistMode, and excludeFromAutoAlign
(none of which bumped the version either).

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🤖 Drafted with Claude Code; reviewed and submitted by a human.