feat(dashboard): wire skills autocomplete configuration to session cards

Connect the skills enumeration API to session card input fields for
slash command autocomplete:

App.js:
- Add skillsConfig state for Claude and Codex skill configs
- Fetch skills for both agent types on mount using Promise.all
- Pass agent-appropriate autocompleteConfig to each SessionCard

SessionCard.js:
- Accept autocompleteConfig prop and forward to SimpleInput
- Move context usage display from header to footer status bar for
  better information hierarchy (activity indicator + context together)

SimpleInput.js:
- Fix autocomplete dropdown padding (py-2 -> py-1.5)
- Fix font inheritance (add font-mono to skill name)
- Fix description tooltip whitespace handling (add font-sans,
  whitespace-normal)

SpawnModal.js:
- Add SPAWN_TIMEOUT_MS (2x default) to handle pending spawn registry
  wait time plus session file confirmation polling

AgentActivityIndicator.js:
- Minor styling refinement for status display

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

dashboard/components/AgentActivityIndicator.js

@@ -92,7 +92,7 @@ export function AgentActivityIndicator({ session }) {
   const tokenDisplay = formatTokens(turnTokens);
 
   return html`
-    <div class="flex items-center gap-2 px-3 py-2 border-b border-selection/50 bg-bg/60 font-mono text-label">
+    <div class="flex items-center gap-2 font-mono text-label">
       ${isActive && html`
         <span class="activity-spinner"></span>
       `}