fix(ui): a reading's age no longer puts a <time> element inside a title attribute (#5467)

The `when` filter returns a <time> element, so title="{{ at|when }}" wrote raw
markup into the attribute. That broke the hover text, and in the rule form's
metric preview (#5475) it leaked a stray `">` into the page. `ago` already
carries the exact time as its own tooltip, so both places drop the title.
Also fixes #5467's page test, which needed the escaped apostrophe.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/core/test_steward_health.py

@@ -55,6 +55,7 @@ async def test_the_page_reads_as_a_verdict_then_each_measure(app, previews):
     async with app.test_request_context("/settings/system/"):
         session["user_role"] = "admin"
         page = " ".join((await render_template("settings/system.html", **got)).split())
-    assert '<span class="tone-warn">Steward wasn\'t watching for up to 7m' in page
+    assert '<span class="tone-warn">Steward wasn&#39;t watching for up to 7m' in page
+    assert 'title="<' not in page          # a <time> element never lands inside an attribute
     assert "Database round trip" in page and "4 ms" in page and "2 ms – 9 ms" in page
     assert page.index("page-verdict") < page.index("Agent posts per minute")