feat(ui): status_badge, status_dot, stat_tile, empty_state, page_header, icon_button and form classes (#5094)

#5094 "Status and layout macros, and form classes".

- formatting.STATES: one state -> (tone, label) map for up, down, stale,
  firing, pending, acknowledged, no_data, ok, warn, crit, resolved and
  inactive; status_info() reads it (an unmapped state is drawn dim under its
  own name). required() lets a macro refuse a missing argument.
- _macros.html: status_badge and status_dot (a dot always carries its label,
  sr-only unless shown), stat_tile, empty_state, page_header (actions via a
  call block) and icon_button, which raises without a label.
- steward.css: tone classes (badge-/dot-/stat- ok, warn, crit, info, dim),
  .sr-only, .page-header, .stat-tile, .empty-state, .btn-icon and the form
  classes .field, .field-label, .field-hint and .input. Info text is a 40%
  mix (--blue): the house --fs-info-fg falls to 4.18:1 on its tint over a
  hovered row, 40% holds 5.09:1.
- First users: the Alerts list, history and maintenance pages (headers,
  state badges, empty states) and the alert forms' hints; the inline inp/lbl
  style sets on the monitor and host forms become .input / .field-label.
- tests/core/test_macros.py renders each macro through the app environment.

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

steward/app.py

@@ -140,6 +140,9 @@ def create_app(
     app.jinja_env.globals["status_class"] = (
         lambda value, kind: _fmt.status_class(value, kind, app.config.get("THRESHOLDS", {}))
     )
+    # The status and layout macros in _macros.html read these.
+    app.jinja_env.globals["status_info"] = _fmt.status_info
+    app.jinja_env.globals["required"] = _fmt.required
 
     # Forged-request protection: every POST form renders csrf_field(), HTMX and
     # fetch() send csrf_token() as X-CSRF-Token, and one check refuses any