Add empty states and loading skeletons across pages

[BunsDev]

Problem

Pages like traces, workflows, artifacts, and memory show blank content when there is no data or while data is loading. This creates a confusing experience — users can't tell if data is loading, if there's an error, or if the page is simply empty.

Proposed Solution

Empty States

Add illustrated empty states with:

• A relevant icon or illustration
• A descriptive message (e.g., "No traces yet")
• A call-to-action where appropriate (e.g., "Run your first ingestion" with a link to docs)

Loading Skeletons

Add skeleton placeholders that match the layout of the actual content:

• Table rows for list pages
• Card placeholders for dashboard
• Text block placeholders for detail pages

Pages to Update

• /dashboard — skeleton for charts and metric cards
• /traces — empty state + table skeleton
• /workflows — empty state + table skeleton
• /artifacts — empty state + grid skeleton
• /memory — empty state + list skeleton
• /investigations — empty state + list skeleton
• /calendar — empty state for days with no activity

Acceptance Criteria

• Every list/table page has a meaningful empty state
• Loading states use skeleton components (shadcn/ui Skeleton already available)
• Empty states include actionable next steps where relevant
• Consistent visual style across all empty states

🤖 Generated with Claude Code