feat: add search, filter, sort, and grid/list view toggle to dashboard

[marko-k0]

Summary

• Add search bar, collapsible filter panel (namespace, bake status, readiness, has-upgrades), and sort dropdown to the rollout list page
• Add list/grid view toggle — list view shows full card details, grid view shows compact multi-column cards for at-a-glance overview
• Add summary stats bar (total, healthy, failing, upgrades available) above the rollout list
• Add color-coded card borders based on bake status and persist all user preferences to localStorage

Test plan

• Verify stats bar shows correct counts matching actual rollout data
• Test search filtering by rollout name, title, and description
• Test namespace/bake status/readiness pill filters toggle on/off correctly
• Test "Has upgrades" filter isolates rollouts with pending upgrades
• Verify sort options (newest/oldest, name A-Z/Z-A, most upgrades) reorder correctly
• Toggle "Group by namespace" on/off and verify grouping behavior
• Switch between list and grid views and verify layout changes
• Verify color-coded borders (left in list, top in grid) match bake status
• Confirm empty state appears when filters match nothing, with working "Clear all filters" button
• Refresh page and verify preferences (filters, sort, view mode) persist via localStorage
• Test responsive layout on mobile (stats 2x2 grid, controls stack vertically)

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