refactor(dashboard): extract modular Preact component structure

Replace the monolithic single-file dashboards (dashboard.html,
dashboard-preact.html) with a proper modular directory structure:

  dashboard/
    index.html              - Entry point, loads main.js
    main.js                 - App bootstrap, mounts <App> to #root
    styles.css              - Global styles (dark theme, typography)
    components/
      App.js                - Root component, state management, polling
      Header.js             - Top bar with refresh/timing info
      Sidebar.js            - Project tree navigation
      SessionCard.js        - Individual session card with status/actions
      SessionGroup.js       - Group sessions by project path
      Modal.js              - Full conversation viewer overlay
      ChatMessages.js       - Message list with role styling
      MessageBubble.js      - Individual message with markdown
      QuestionBlock.js      - User question input with quick options
      EmptyState.js         - "No sessions" placeholder
      OptionButton.js       - Quick response button component
      SimpleInput.js        - Text input with send button
    lib/
      preact.js             - Preact + htm ESM bundle (CDN shim)
      markdown.js           - Lightweight markdown-to-HTML renderer
    utils/
      api.js                - fetch wrappers for /api/* endpoints
      formatting.js         - Time formatting, truncation helpers
      status.js             - Session status logic, action availability

This structure enables:
- Browser-native ES modules (no build step required)
- Component reuse and isolation
- Easier styling and theming
- IDE support for component navigation

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

dashboard/utils/formatting.js

@@ -0,0 +1,66 @@
+// Formatting utilities
+
+export function formatDuration(isoStart) {
+  if (!isoStart) return '';
+  const start = new Date(isoStart);
+  const now = new Date();
+  const mins = Math.max(0, Math.floor((now - start) / 60000));
+  if (mins < 60) return mins + 'm';
+  const hrs = Math.floor(mins / 60);
+  const remainMins = mins % 60;
+  return hrs + 'h ' + remainMins + 'm';
+}
+
+export function formatTime(isoTime) {
+  if (!isoTime) return '';
+  const date = new Date(isoTime);
+  return date.toLocaleTimeString('en-US', {
+    hour: 'numeric',
+    minute: '2-digit',
+    hour12: true
+  });
+}
+
+export function formatTokenCount(value) {
+  if (!Number.isFinite(value)) return '';
+  return Math.round(value).toLocaleString('en-US');
+}
+
+export function getContextUsageSummary(usage) {
+  if (!usage || typeof usage !== 'object') return null;
+
+  const current = Number(usage.current_tokens);
+  const windowTokens = Number(usage.window_tokens);
+  const sessionTotal = usage.session_total_tokens != null ? Number(usage.session_total_tokens) : null;
+  const hasCurrent = Number.isFinite(current) && current > 0;
+  const hasWindow = Number.isFinite(windowTokens) && windowTokens > 0;
+  const hasSessionTotal = sessionTotal != null && Number.isFinite(sessionTotal) && sessionTotal > 0;
+
+  if (hasCurrent && hasWindow) {
+    const percent = (current / windowTokens) * 100;
+    return {
+      headline: `${percent >= 10 ? percent.toFixed(0) : percent.toFixed(1)}% ctx`,
+      detail: `${formatTokenCount(current)} / ${formatTokenCount(windowTokens)}`,
+      trail: hasSessionTotal ? `Σ ${formatTokenCount(sessionTotal)}` : '',
+      title: `Context window usage: ${formatTokenCount(current)} / ${formatTokenCount(windowTokens)} tokens`,
+    };
+  }
+
+  if (hasCurrent) {
+    const inputTokens = Number(usage.input_tokens);
+    const outputTokens = Number(usage.output_tokens);
+    const hasInput = Number.isFinite(inputTokens);
+    const hasOutput = Number.isFinite(outputTokens);
+    const ioDetail = hasInput || hasOutput
+      ? ` • in ${formatTokenCount(hasInput ? inputTokens : 0)} out ${formatTokenCount(hasOutput ? outputTokens : 0)}`
+      : '';
+    return {
+      headline: 'Ctx usage',
+      detail: `${formatTokenCount(current)} tok${ioDetail}`,
+      trail: '',
+      title: `Token usage: ${formatTokenCount(current)} tokens`,
+    };
+  }
+
+  return null;
+}