Web: visual design pass (issue #26)

Addresses the screenshot-review feedback in #26. No framework or build
step added — all of this stays within the existing plain HTML/CSS/
vanilla-JS + go:embed architecture.

- Nav: re-enable the bottom tab bar that was already built and
  switched off (Queue/On-call/Alerts/Team + a "More" sheet for
  Stats/Admin/Account), replacing the hamburger on phone width.
- Queue: chip counts, a scroll fade on the filter row, a
  "Triggered Xh ago" + severity label per row, a chevron on the team
  switcher so it reads as a dropdown.
- On-call: collapse repeated same-person days into shift bars (week
  view and "your shifts" both), show the week as a date range with
  the ISO week number as secondary text, split "Current shift" out
  from "Next shifts" with "ends in Nd", a pill badge + row highlight
  for "you".
- Incident detail: fix the actual bug behind the duplicate
  "acknowledged" timeline entries (acknowledgeIncident's UPDATE had no
  guard on the incident's current status, so acknowledging an
  already-acknowledged incident silently re-logged the event — now
  idempotent, with regression tests on both the authenticated route
  and the ntfy ack-button route). Relabel escalation re-pages so they
  don't look like the same page landing twice. Copy the primary action
  up near the top. Label the "···" button. Group the timeline by
  phase (triggered/acknowledged/resolved). Add an "at a glance"
  summary row (duration/severity/responsible) and collapse the group
  labels by default.
- Team overview: reword the vague copy ("One owner." etc.) into plain
  labels.
- Empty states: fill in missing icons/one-liners across queue,
  alerts, stats and the incident timeline.
- CSS: fix card padding bugs, verify link contrast already passes AA,
  introduce a --fs-* type-scale token set and migrate the few
  genuinely isolated cases onto it (left sizes tied to a fixed shape,
  a deliberately prominent display, or a non-negotiable constraint
  like the iOS-zoom-prevention input size as documented exceptions
  rather than guess at a render this change can't see).

Verified with the full fmt/lint/test/helm-lint gate, plus a live
instance against the test DB with seeded incidents and schedule data
to trace the on-call grouping and timeline phase-splitting logic
against real API responses.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

internal/api/notify_test.go

@@ -408,6 +408,47 @@ func TestNotify_AckButtonAcknowledgesIncident(t *testing.T) {
 	}
 }
 
+// The ack token isn't single-use (it stays valid for a day, in case the
+// first tap never reaches the server), so tapping the same notification's
+// Acknowledge button twice is a real scenario, not just a retried request.
+// It must report the incident's actual state, not assume "resolved" —
+// see handleNotifyAck's !acked branch — and must not log a second
+// "acknowledged" event.
+func TestNotify_AckButtonTwiceIsIdempotent(t *testing.T) {
+	s, f := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
+
+	fireCritical(t, s)
+	s.sweepNotify(t)
+
+	ackURL := f.messages()[0].Actions[0].URL
+	path := ackURL[strings.Index(ackURL, "/api/notify/ack/"):]
+
+	for i := range 2 {
+		resp, err := http.Post(s.URL+path, "application/json", nil)
+		if err != nil {
+			t.Fatalf("ack %d: %v", i+1, err)
+		}
+		var body map[string]any
+		decode(t, resp, &body)
+		if resp.StatusCode != http.StatusOK {
+			t.Fatalf("ack %d returned %d", i+1, resp.StatusCode)
+		}
+		if body["status"] != "acknowledged" {
+			t.Errorf("ack %d: expected status acknowledged, got %v", i+1, body["status"])
+		}
+	}
+
+	n := 0
+	for _, ty := range eventTypes(timeline(t, s, 1)) {
+		if ty == "acknowledged" {
+			n++
+		}
+	}
+	if n != 1 {
+		t.Errorf("expected exactly one acknowledged event after two taps, got %d", n)
+	}
+}
+
 func TestNotify_AckRejectsUnknownToken(t *testing.T) {
 	s, _ := notifyTS(t, api.NotifyConfig{PublicURL: "https://terdut.example.com"})
 	fireCritical(t, s)