ifcviewer-web: draw the axis indicator (corner gizmo + orbit pivot)

The desktop viewport draws an RGB triad in the bottom-left corner and a
second one at the orbit target while navigating; the web build drew
neither. Both lived in the Qt-coupled OverlayRenderer, which only
ViewportWindow drives — the web host no-ops the overlay hooks — so the
wasm build had no path to them at all.

Lift them into AxisIndicatorRenderer, a Qt-free renderer in
IfcViewerCore, and drive it from ViewportCore::render for desktop and
web alike. Same move SectionGizmoRenderer already made; the drawing code
is unchanged apart from swapping qDegreesToRadians for CameraMath's kPiF.

Pivot visibility moves to the core with it: it was a QTimer on
ViewportWindow, so the afterglow couldn't follow the gizmo across. It is
now a Stopwatch deadline next to the drawing, with render() requesting
frames until an armed afterglow expires. Hosts keep the same three
triggers (on for orbit/pan drags, off on release, 600 ms on wheel).

The web demo shell's log overlay sat exactly on top of the corner gizmo,
so it shifts right of the 110 px box.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/ifcviewer-web/web/IfcViewerWeb.html

@@ -12,8 +12,10 @@
      eats pointer events so the drag keeps reaching the canvas. */
   #marquee { position: fixed; display: none; z-index: 50; pointer-events: none;
     border: 1px solid #4a9eff; background: rgba(74, 158, 255, 0.15); }
-  /* Log overlay sits bottom-left and never eats pointer events. */
-  #status { position: fixed; bottom: 8px; left: 12px;
+  /* Log overlay sits bottom-left and never eats pointer events. Kept clear
+     of the corner axis gizmo, which the viewport draws in the bottom-left
+     110 CSS px (plus a 10 px margin). */
+  #status { position: fixed; bottom: 8px; left: 132px;
     max-width: min(60vw, 680px); max-height: 28vh; overflow-y: auto;
     font-size: 11px;
     font-family: ui-monospace, "Cascadia Mono", Menlo, Consolas, monospace;