fix(vscode): keep deleted diff bars visible

[marius-kilocode]

What Problem This Solves

Pierre deletion bars could disappear when the host did not provide a complete background token set. Deleted line numbers could also inherit the deletion color instead of the neutral gutter color.

Why This Change Was Made

Use Pierre's dedicated deletion-number override and provide a Kilo semantic fallback for the deletion background. Keep Kilo's existing diff surfaces and explicitly use the vertical bars indicator mode.

User Impact

Deleted changes now show a visible red gutter bar while deleted line numbers remain neutral across light, dark, and high-contrast VS Code themes.

Evidence

The isolated VS Code self-test harness rendered a real Agent Manager local diff. Computed styles showed a visible 4px deletion bar with a red gradient, and deleted line-number color matched the context line-number color in Visual Studio dark, Ayu dark, GitHub dark high contrast, and GitHub light high contrast themes.

The automated visual matrix passed 36 cases across all configured VS Code themes and narrow and wide layouts. The extension unit suite passed 5,179 tests, with 2 skipped.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• .changeset/neutral-deleted-line-numbers.md
• packages/kilo-ui/src/pierre/index.ts
• packages/kilo-ui/src/pierre/index.test.ts
• packages/kilo-ui/tests/diff-indicators.spec.ts

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_{Reviewed by grok-4.6 · Input: 76.1K · Output: 20.5K · Cached: 844.5K}

_{Review guidance: REVIEW.md from base branch main}