kg: explore-page camera-fit zooms to entire graph, not the path

[jung-thomas]

Follow-up from PR #687 (Track 3-B Task 5).

After clicking 'Find path' in /explore/, the camera calls renderer.getCamera().animatedReset() which re-centers on the entire graph, guaranteeing the path is visible but not zoomed to it. For a 1700-node graph the path is hard to spot.

Change

In app/explore/src/components/ExploreGraph.vue, replace animatedReset() with a bounding-box compute over the path nodes:

// Compute the bounding box of path nodes
const pathNodes = newPath.map(id => graph.getNodeAttributes(id))
const xs = pathNodes.map(n => n.x).filter(x => Number.isFinite(x))
const ys = pathNodes.map(n => n.y).filter(y => Number.isFinite(y))
if (xs.length && ys.length) {
  const minX = Math.min(...xs), maxX = Math.max(...xs)
  const minY = Math.min(...ys), maxY = Math.max(...ys)
  const centerX = (minX + maxX) / 2
  const centerY = (minY + maxY) / 2
  const ratio = Math.max(maxX - minX, maxY - minY) / 2 || 0.5
  renderer.getCamera().animate({ x: centerX, y: centerY, ratio }, { duration: 600 })
}

Verify against Sigma v3's actual camera API — getCamera().animate(target, options) is the documented method.

Acceptance

• After clicking 'Find path', the camera animates to fit the path's bounding box with some padding.
• Edge case: path of length 1 (impossible — path always has ≥2 nodes) → no-op.
• Test (or PR 6 manual smoke check) confirms the path is visibly highlighted in the camera viewport.