Prevent Info Pane overlap in narrow windows

[raisulchowdhury]

Summary

• centralize the minimum widths used by the main window, sidebar, and Info Pane
• include the Info Pane's column spacing, horizontal margins, and split-view divider in the window minimum
• prevent the two Info Pane columns from overlapping when the window is resized narrower

Validation

• before the change, the window accepted a requested size of 600 × 500 and the Info Pane content overlapped
• after the change, the same resize request is clamped to 907 × 500
• xcodebuild test -project Xcodes.xcodeproj -scheme Xcodes -destination 'platform=macOS,arch=arm64' -quiet

Fixes #823.

AI assistance

An AI coding agent helped reproduce the issue and prepare the initial patch. A separate primary-agent review corrected the width calculation to include SwiftUI's column spacing, inspected the final diff, reran the macOS test suite, and verified the window's runtime minimum size.

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