fix(vscode): move prompt rail away from session content

[marius-kilocode]

The prompt navigator rail currently tracks the centered readable lane. On wide sessions, that places its hover targets beside the content the pointer naturally crosses, making the navigator easy to open accidentally. In Agent Manager, the same placement also sits close to the sidebar splitter.

This change anchors the rail to the chat panel edge with an 8px splitter-safe gutter, suppresses hover activation while a button is held so resize and text-selection drags cannot open the navigator, and uses compositor-friendly tick transforms while preserving the existing rendered sizes.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

lgtm — the buttons !== 0 guard targets the real event path (the Agent Manager resize handle uses document-level mousemove without pointer capture, so ticks do receive mouseenter mid-drag), and the transform-based tick sizing was verified state-by-state against the previous pixel sizes (rest 9×1.5px, active 13×1.5px, hover/focus 16×2px) with the overflow-tick specificity interactions intact. Changeset is present and user-facing; existing PromptRail Storybook stories cover the new positioning.

Files Reviewed (3 files)

• .changeset/prompt-rail-panel-edge.md
• packages/kilo-vscode/webview-ui/src/components/chat/PromptRail.tsx
• packages/kilo-vscode/webview-ui/src/styles/prompt-rail.css

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_{Reviewed by kimi-k3 · Input: 77.3K · Output: 16.9K · Cached: 1M}

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