feat(graph-ui): URL routing, filter panel UX, and camera fly-to fix

[rarepops]

Summary

Improvements to the graph UI: the left filter panel is reworked, the active tab and selected project are now reflected in the URL, the camera fly-to no longer snaps back to centre, and a few confusing labels are clarified.

All changes are scoped to graph-ui/. No server or protocol changes.

Changes

Filter panel and folder tree

• Cap the filter panel height and move the node/edge chips into a scroll area, so a long list of types no longer pushes the folder tree off screen.
• Regroup the chips under Node types and Relationships, and pin the Show labels toggle as a footer.
• Add a Folders heading (en/zh) above the folder tree so that section is clearly labelled.

URL routing

• The active tab and selected project are stored in the URL query string (?tab=...&project=...), so the view survives refreshes and can be bookmarked or shared. Back/forward is handled via popstate.
• Query params are used rather than path segments because the embedded HTTP server only serves index.html at / (path routes would 404 on refresh).

Graph tab and HUD

• The Graph tab is disabled until a project is selected, and opening the Projects tab clears the active project.
• The empty-state hint now points at the Projects tab (it previously referenced a "Stats" tab that no longer exists).
• The ambiguous Clear button in the graph HUD is renamed Clear selection so it reads distinctly from Refresh.

Camera fly-to fix

• Focusing a node or cluster only moved the camera and called lookAt, leaving the OrbitControls pivot at the origin. OrbitControls re-centred the view on the next frame, snapping the camera back once the animation ended.
• The controls target is now lerped to the focus point as well, so the view stays on the clicked node and orbits around it afterwards.

Screenshots

• Filter panel (grouping):

• URL routing (address bar showing ?tab / project):

Testing

• npm run build (tsc typecheck + vite build): passing
• npm test (vitest): 8/8 passing
• Manual: deep-link /?tab=graph&project=<name> restores the view; the Projects tab clears the selection and disables the Graph tab; browser back/forward round-trips; the camera stays on the focused node.

Follow-up (not in this PR)

• Persisting the active filter selection (disabled node/edge types plus show-labels) in the URL.