feat(tabs): orbit the working ring around a busy session tab's dot

The desktop home rail and the phone overview both draw a spinning
`tab-load-spin` ring around their green dot while a session works; the
tab strip itself only pulsed. Same ring on the tab dot now, so "working"
reads identically on every surface.

Drawn as a ::after border circle rather than a halo: the skin block sets
`box-shadow: none` on .tab-status.busy to keep tab dots quiet and
outranks any plain class rule, and a pseudo-element sidesteps that
without reintroducing the glow. It is absolutely positioned, so it never
widens the tab or shifts the label, and it is disabled under
prefers-reduced-motion.

Phones keep their existing tell (a 9px dot with a glow) and suppress the
ring: a 15px ring inside a 32px tab would sit on top of the tab name.

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

src/web/public/mobile.css

@@ -680,6 +680,13 @@ html.mobile-init .file-browser-panel {
     box-shadow: 0 0 8px 2px color-mix(in srgb, var(--green) 55%, transparent) !important;
   }
 
+  /* No orbiting ring on phone tabs (styles.css draws one on desktop/tablet):
+     the dot is already enlarged to 9px with a glow here, and a 15px ring in a
+     32px tab would sit on top of the tab name. The glow is the phone's tell. */
+  .session-tab .tab-status.busy::after {
+    display: none;
+  }
+
   /* Truncate tab names more aggressively on mobile */
   .session-tab .tab-name {
     max-width: 50px;

src/web/public/styles.css

@@ -1316,11 +1316,30 @@ html[data-line-anim="packet"] .connection-line.line-enter {
 
 .session-tab .tab-status.idle { background: var(--green); }
 .session-tab .tab-status.busy {
+  position: relative;
   background: var(--green);
   animation: pulse 1.5s infinite;
   /* Performance: GPU acceleration for animation */
   will-change: opacity;
 }
+/* Orbiting ring on a WORKING tab: the same `tab-load-spin` circle the desktop
+   home rail (.home-sessions-dot--working) and the phone overview
+   (.mobile-overview-dot--working) draw, so "working" reads identically on every
+   surface. Pseudo-element on purpose — the skin block below sets
+   `box-shadow: none` on .tab-status.busy to keep tab dots halo-free, and it
+   outranks any plain class rule here; a ring drawn with a border is untouched by
+   that and keeps the tabs quiet while still showing motion. Absolutely
+   positioned, so it never widens the tab or shifts the label. */
+.session-tab .tab-status.busy::after {
+  content: '';
+  position: absolute;
+  inset: -3px;
+  border: 1.5px solid color-mix(in srgb, var(--green) 25%, transparent);
+  border-top-color: var(--green);
+  border-radius: 50%;
+  animation: tab-load-spin 0.7s linear infinite;
+  pointer-events: none;
+}
 
 .session-tab .tab-status.error { background: var(--red); }
 .session-tab .tab-status.ended { background: var(--text-muted); opacity: 0.5; }
@@ -14298,6 +14317,7 @@ html[data-skin="daylight-blue"] .welcome-btn-tunnel.active:hover {
 }
 
 @media (prefers-reduced-motion: reduce) {
+  .session-tab .tab-status.busy::after,
   .home-sessions-row,
   .home-sessions-dot,
   .home-sessions-dot::after {