Replace map overlays with a two-surface workspace

[jonashertner]

Outcome

Reframes Riverflow as two coordinated surfaces so the map remains fully visible and the evidence stays readable.

• persistent evidence workspace beside the map on desktop and landscape screens
• non-overlapping map/workspace stack on portrait screens
• controls, modes, hover readout, source notes, detail views and intro moved off the map
• compact, horizontally scrollable mode rail on narrow screens
• corrected pointer coordinates for the offset canvas
• concise intro copy across DE, EN, FR, IT and RM
• explicit verification contracts for the new layout

Responsive review

Verified at 320×568, 390×844, 768×1024, 844×390, 1280×800, 1536×960 and 2048×1280. Also checked every locale at phone width and the longest translations in short landscape. No document or navigation overflow was found.

Verification

• npm run release
• npm audit --json — 0 vulnerabilities
• git diff --check
• npm run check:links — 79 checked, 0 dead; 2 transient external responses were inconclusive

This stays a draft for an independent design and code review before production.