StammbaumNode gains an optional `dimmed` prop that sets group-level
opacity (DIMMED_OPACITY) on the node's root <g>, so the box, accent bar,
name, and dates fade together as one unit. A lineage-fade CSS transition
eases the change and is neutralised under prefers-reduced-motion. The
selected-node styling (active fill + mint accent bar) is untouched.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Extract the three SVG connector layers (+ the parent-link graph computation)
into StammbaumConnectors.svelte and the node <g> into StammbaumNode.svelte (which
now owns its own focus-ring state). StammbaumTree drops 546→308 lines and is now
an orchestrator: layout, gutter/reduced-motion state, viewBox, gestures, rail,
anchor. Rendered SVG is byte-identical, so the existing browser tests are
unchanged. Verified live: 62 nodes + 58 connector lines render, node-tap selects.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
