feat(dashboard): add working indicator for active sessions

Visual feedback when an agent is actively processing:

1. **Spinner on status dots** (SessionCard.js, Modal.js)
   - Status dot gets a spinning ring animation when session is active/starting
   - Uses CSS border trick with transparent borders except top

2. **Working indicator in chat** (ChatMessages.js, Modal.js)
   - Shows at bottom of conversation when agent is working
   - Bouncing dots animation ("...") next to "Agent is working" text
   - Only visible for active/starting statuses

3. **CSS animations** (styles.css)
   - spin-ring: 0.8s rotation for the status dot border
   - bounce-dot: staggered vertical bounce for the working dots

4. **Status metadata** (status.js)
   - Added `spinning: true` flag for active and starting statuses
   - Used by components to conditionally render spinner elements

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dashboard/components/Modal.js

@@ -132,7 +132,7 @@ export function Modal({ session, conversations, conversationLoading, onClose, on
             <div class="mb-1 flex items-center gap-3">
               <h2 class="truncate font-display text-xl font-semibold text-bright">${session.project || session.name || session.session_id}</h2>
               <div class="flex items-center gap-2 rounded-full border px-2.5 py-1 text-xs ${status.badge}">
-                <span class="h-2 w-2 rounded-full ${status.dot}"></span>
+                <span class="h-2 w-2 rounded-full ${status.dot} ${status.spinning ? 'spinner-dot' : ''}" style=${{ color: status.borderColor }}></span>
                 <span class="font-mono uppercase tracking-[0.14em]">${status.label}</span>
               </div>
               <span class="rounded-full border px-2.5 py-1 font-mono text-micro uppercase tracking-[0.14em] ${agent === 'codex' ? 'border-emerald-400/45 bg-emerald-500/14 text-emerald-300' : 'border-violet-400/45 bg-violet-500/14 text-violet-300'}">
@@ -178,6 +178,15 @@ export function Modal({ session, conversations, conversationLoading, onClose, on
             <p class="text-dim text-center py-12">No conversation messages</p>
           `}
         </div>
+        ${status.spinning && html`
+          <div class="shrink-0 flex items-center gap-2 border-t border-selection/40 bg-surface px-5 py-2">
+            <span class="h-2 w-2 rounded-full spinner-dot" style=${{ backgroundColor: status.borderColor, color: status.borderColor }}></span>
+            <span class="font-mono text-xs" style=${{ color: status.borderColor }}>Agent is working</span>
+            <span class="working-dots font-mono text-xs" style=${{ color: status.borderColor }}>
+              <span>.</span><span>.</span><span>.</span>
+            </span>
+          </div>
+        `}
 
         <!-- Modal Footer -->
         <div class="border-t border-selection/70 bg-bg/55 p-4">