feat(alerts): history reads as episodes; tests follow the confirm dialog (#5316, #5314)

History (#5316):
- Transitions fold into episodes (steward/alerts/episodes.py): each stretch
  out of quiet, the worst state it reached, how long it lasted, its worst
  reading against the rule ('3m 21s (fires above 3m)'), who was told across
  its changes, and its Ansible runs. The changes themselves fold under it.
- An episode cut by paging says so ('cleared later (above)', 'earlier').
- For one rule: a verdict ('Fired 4 times in the last 7d, 1h 2m in all') and
  no Rule column. Notified and Action show only when the range has any.

Tests:
- The confirm guard looks for a confirm( call, not the word in the comment
  that says it is gone (lesson #4365).
- The Hosts viewer test looks for the add-host dialog by id, since every page
  now carries the confirm dialog.

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

tests/core/test_host_page.py

@@ -127,7 +127,7 @@ async def test_add_host_is_a_dialog_on_the_hosts_list(app):
     async with app.test_request_context("/hosts/"):
         session["user_role"] = "viewer"
         viewer = await render_template("hosts/list.html", **_list_ctx(add={}))
-    assert "<dialog" not in viewer and ">Add host<" not in viewer
+    assert 'id="add-host"' not in viewer and ">Add host<" not in viewer
 
 
 async def test_add_host_sends_a_clash_back_with_what_was_typed(app):