feat(app): register timeago Jinja filter

Templates can now call {{ ts | timeago }} directly without route-side
precomputation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

l4d2web/l4d2web/app.py

@@ -28,6 +28,7 @@ from l4d2web.services.job_worker import (
     start_state_poller,
 )
 from l4d2web.services.live_state_poller import start_live_state_poller
+from l4d2web.services.timeago import format_time_html
 
 
 def _in_flask_cli_context() -> bool:
@@ -58,6 +59,8 @@ def create_app(test_config: dict[str, object] | None = None) -> Flask:
     with app.app_context():
         init_db()
 
+    app.add_template_filter(format_time_html, "timeago")
+
     @app.before_request
     def csrf_protect() -> Response | None:
         if "csrf_token" not in session:

l4d2web/tests/test_timeago.py

@@ -115,3 +115,19 @@ def test_format_time_html_normalises_naive_input_to_utc():
     out = str(format_time_html(then_naive, now=now))
     assert 'datetime="2026-05-16T14:32:11+00:00"' in out
     assert 'title="2026-05-16 14:32:11 UTC"' in out
+
+
+def test_timeago_filter_registered_on_app():
+    from flask import render_template_string
+
+    from l4d2web.app import create_app
+
+    app = create_app({"TESTING": True, "SECRET_KEY": "test"})
+    with app.app_context():
+        rendered = render_template_string(
+            "{{ ts | timeago }}",
+            ts=datetime.now(UTC) - timedelta(minutes=3),
+        )
+    assert "<time " in rendered
+    assert "&lt;time" not in rendered
+    assert "3 minutes ago" in rendered