feat(chat): quick-action buttons in empty state

[vybe]

Context

Client feedback (Paradigm Life, April 2026) noted that the empty chat state provides no guidance on what to type, creating high activation energy for new/occasional users.

Current State

ChatMessages.vue empty state shows generic "Start a Conversation" message with no actionable suggestions.

Requested

Replace blank canvas with quick-action buttons for top use cases that trigger playbooks or common queries.

Acceptance Criteria

• Empty state displays 4-6 suggested action buttons
• Buttons map to agent's available playbooks (if any)
• Fallback to generic suggestions if no playbooks defined
• Clicking a button populates input or sends directly
• Works in PublicChat view (uses public playbook endpoint)

Validation Required

• Confirm playbook data is available at chat load time
• Decide: pre-populate input vs send immediately on click

Design Reference

Claude.ai shows suggested prompts in empty state. Similar pattern requested.

References

• Client feedback: "Blank canvas after intro — no guidance"
• Client recommendation: "Add quick-action buttons for top 4–6 use cases"
• Effort: Low-Medium
• Priority: High (reduces activation energy)

/label enhancement,ui,P1b

[vybe]

Shipped in v0.6.0 (released via #998).