chore(webui): remove timeline animation page

The animated t-SNE 'embedding landscape' added no real analytical value and
its cumulative-by-month logic was inherently confusing (ancient drafts
appearing late in the animation). Removed entirely rather than maintained.

Drops the /timeline route, template, nav link, data builder
(get_timeline_animation_data / _compute_timeline_animation_data) and its test.
The Overview mini-timeline and /api/timeline (separate features) are untouched.

src/webui/data/__init__.py

@@ -69,7 +69,6 @@ from webui.data.analysis import (  # noqa: F401
     get_timeline_data,
     get_similarity_graph,
     get_idea_clusters,
-    get_timeline_animation_data,
     get_monitor_status,
     get_citation_graph,
     get_landscape_tsne,