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/blueprints/pages.py

@@ -11,7 +11,6 @@ from webui.data import (
     get_draft_detail,
     get_rating_distributions,
     get_timeline_data,
-    get_timeline_animation_data,
     get_ideas_by_type,
     get_top_authors,
     get_org_data,
@@ -127,12 +126,6 @@ def ratings():
     )
 
 
-@pages_bp.route("/timeline")
-def timeline_animation():
-    data = get_timeline_animation_data(db())
-    return render_template("timeline.html", animation=data)
-
-
 @pages_bp.route("/idea-clusters")
 def idea_clusters():
     data = get_idea_clusters(db())