🐞 Keep PDF navigation accessible in split view

[JFWooten4]

Problem

In a constrained split-view panel, a host-provided control at the lower-right corner can obscure the minimap's controls (including collapse/expand). The footnote scrubber can extend into the same interactive area. The More PDF tools menu also has no height cap, so lower settings such as Show minimap and footnote/navigation options can extend beyond shorter panels.

Changes

• Reserve 48px of bottom clearance at viewer widths up to 1200px, keeping expanded/collapsed minimap controls clear of the lower-right overlay. Reflect that clearance in the native scrollbar track.
• In the same constrained widths, inset the footnote scrubber's right-hand control area to prevent a split-view overlay from intercepting scrubber interaction.
• Constrain the PDF tools dropdown to the viewport's dynamic height and make its content scrollable so the minimap and footnote options remain reachable.
• Add regression assertions for the split-view clearance and viewport-bounded tools menu.

Verification

• Confirmed the commit contains changes to exactly three intended files, and the proposed Git tree differs from main.
• Checked CSS rules against regression assertions for the split-view safe clearance, footnote scrubber and menu scrolling.
• Not visually verified in a live split-view host; please check expanded/collapsed minimap, the footnote scrubber, scrolling all tools menu settings, and full-window behavior.

Screenshot provided in the originating discussion demonstrates the lower-right overlay.