CSS: convert all topology inline styles to modifier classes

Replace style= attributes on topology wire/node elements with semantic
modifier classes:
- topo-vc-wire--wan, --10g, --mgmt (wire colour semantics in CSS)
- topo-v2-host--bus (bus-section node size constraint)
- topo-legend-item--offrack already done in prior commit

Zero inline styles remain in the topology section.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

static/style.css

@@ -410,6 +410,9 @@
   background: linear-gradient(to bottom, var(--cyan), var(--green));
   opacity: .7;
 }
+.topo-vc-wire--wan  { background: linear-gradient(to bottom, var(--cyan), rgba(0,212,255,.3)); opacity: .7; }
+.topo-vc-wire--10g  { background: var(--amber); opacity: .6; }
+.topo-vc-wire--mgmt { background: var(--border-color); opacity: .5; }
 /* Blurred copy of the wire for a soft glow halo */
 .topo-vc-wire::before {
   content: '';
@@ -467,6 +470,7 @@
 .topo-v2-sub   { font-size: .58em; color: var(--text-muted); letter-spacing: .02em; }
 .topo-v2-vlan  { font-size: .54em; color: var(--cyan); opacity: .75; }
 
+.topo-v2-host--bus { min-width: 80px; max-width: 96px; }
 .topo-v2-internet { border-color: var(--cyan);  color: var(--cyan);  text-shadow: var(--glow-cyan); box-shadow: 0 0 12px rgba(0,212,255,.12); }
 .topo-v2-router   { border-color: var(--cyan);  color: var(--cyan);  text-shadow: var(--glow-cyan); box-shadow: 0 0 12px rgba(0,212,255,.14); }
 .topo-v2-switch   { border-color: var(--amber); color: var(--amber); text-shadow: var(--glow-amber); box-shadow: 0 0 12px rgba(255,179,0,.12); }