[v0.5] Eliminate phantom horizontal shelf scrolling at narrow/high-DPI widths

[JUhalt]

Goal

Remove unnecessary horizontal manuscript-shelf scrolling that can remain at narrow window sizes or high Windows DPI after v0.3 responsive-layout hardening.

Context

v0.3 certification confirmed that all manuscript-card actions remain visible/reachable and the board remains usable at 100%, 125%, and 150% scaling. Some shelf containers can still expose horizontal scroll range into empty space.

Acceptance

• No phantom horizontal scroll range when all shelf content fits.
• Vertical scrolling remains intact.
• Open, Move/Restore, Delete, and View Route remain reachable.
• 100%, 125%, and 150% minimum-width smoke tests pass.
• No regression to keyboard navigation or resizing.

[JUhalt]

This visual follow-up is being brought forward alongside v0.5 at the user's request and moved into that milestone for traceability.

The defect is reproduced: after narrowing a populated shelf, its viewport can be 819 pixels wide while WinForms retains a 1062-pixel display width from the previous layout, leaving horizontal scrolling into empty space. A targeted layout invalidation fix is in progress; it does not hide scrollbars or remove genuine vertical overflow.

Checks cover repeated wide/narrow resizing, populated/empty transitions, vertical scrolling, and card-action reachability. Native 100%/125%/150% evidence remains an acceptance requirement; simulated scaled layout tests will be reported separately. The issue stays open pending verification.