[milanb17]

What changed

• Stage width floor. An animation's stage lays out at least 720px wide (STAGE_MIN_WIDTH), the board's reading width. On a full-size board it fits with no horizontal scroll; in a narrower block it keeps 720px and scrolls sideways instead of squeezing the drawing. Wider boards and fullscreen still give it more room, and fullscreen scales from at least 720px.
• Scene gap gives way first. The column gap a row's link label opens (up to 160px) now shrinks back toward 48px when the columns would otherwise overflow. Cards keep their 140px minimum. The scene only overflows when even the normal gap can't fit, and the layout reruns on resize.
• Labels avoid other lines. Label placement now treats every other visible arrow's line as an obstacle. A two-way link between the same cards is fanned 9px apart, and the outbound label used to sit on the return line.
• Authoring instructions. animation.md tells agents to draw for a 720px stage with nothing past its right edge, and not to shrink the drawing for narrow windows.

Why

A three-column scene with long labels asked for about 778px. The board's column is about 755px at any window width, so the right column was cut off even in a wide window. In the same board, the "Import link" label had the return arrow running through it.

Testing

• New browser tests: a three-column scene with long labels fits the block (fails on main), a link's label stays off the parallel return line (fails on main), and a small drawing in a 480px block gets a 720px stage that scrolls.
• The six-column scroll test is reworded and no longer checks the label gap, which now gives way when the scene overflows.
• The block and animation browser suites (109 tests) and the instruction node tests pass. Lint, format and typecheck pass.
• Not yet checked in an isolated Desktop.