feat(dashboard): add section header tiles with analytics

[justinsunyt]

Problem

Dashboard users need a first-class way to group tiles into sections without learning the generic text tile markdown and transparency settings.

Changes

• Added a section header mode backed by text tiles, storing section titles as H1 markdown with transparent backgrounds.
• Added full-width section layouts by default on sm and xs, including layout fallback behavior for section-like text tiles without stored layouts.
• Added section header options to the dashboard Add menu and the empty dashboard Get started menu.
• Polished section rendering and the section creation/edit modal, and recorded analytics when sections are added or rearranged.

How did you test this code?

Agent-tested with:

• hogli test frontend/src/lib/components/Cards/TextCard/textCardModalLogic.test.ts frontend/src/lib/components/Cards/TextCard/TextCard.test.tsx frontend/src/scenes/dashboard/EmptyDashboardComponent.test.tsx frontend/src/scenes/dashboard/tileLayouts.test.ts
• pnpm --filter=@posthog/frontend format
• pnpm --filter=@posthog/frontend typescript:check
• pnpm --filter=@posthog/frontend build:products
• Live Playwright verification against local PostHog: created a dashboard, used Add → Section header, confirmed the tile stored # Activation with transparent background and full-width sm/xs layouts, dragged the section in edit mode, and observed both dashboard section header added and dashboard section header rearranged captures.

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

Docs update

No docs update needed.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Implemented by Capy. I kept sections on the existing text-tile model rather than adding a new tile type, so persistence, editing, duplication, and dashboard layout flows continue to use the existing dashboard tile system.

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