Sidebar search and filter bar for plan site

Acceptance Criteria

• Text input appears at the top of the sidebar
• Typing filters items by matching against ID, title, tags, assignee, milestone
• field:value syntax works (e.g., status:ready, priority:high, tags:css)
• Multiple filters combine with AND logic; multiple values for same field use OR
• Escape clears the filter
• / keyboard shortcut focuses the filter input
• Filtering auto-expands matching groups (works with WORK-044)
• Nav items include data-tags, data-priority, data-severity, data-assignee, data-milestone attributes

Approach

Client-side behavior (~2KB). All data is already in the DOM via data attributes on nav items (added in WORK-038). No server round-trip needed. The behavior reads data attributes and filters by toggling visibility.

References

• Plan Site UX at Scale (Plan Site UX at Scale — Feature 2)
• Build nav region builder for plan site (nav region builder — provides data attributes)
• Collapsible status groups in plan sidebar (collapsible groups — filtering interacts with collapse state)