feat(visualize): radial mind-map — pick a node, fan out level by level

Replace the indented outline with a real radial mind-map (what was asked
for: a centre that radiates outward, layer by layer):
- BFS spanning tree from a root over the wikilinks → each node has one
  parent, so it's a clean tree (not the 800-edge mesh); branches fan out
  on rings by depth, angular space allocated by subtree size
- bounded for readability on a dense graph: depth <= 2 and <= 14 branches
  per node (highest-degree kept), long labels truncated, auto-fit zoom
  with a readable floor
- click any node → it becomes the new centre and re-fans (this is the
  "某个点发散出去" exploration); panel shows its details/sources/links;
  spacing slider stretches the rings; reset returns to the top hub
- MIND-MAP <-> 3D GRAPH toggle retained
Removes the provenance outline tree.

Author: KylinMountain