Empty states across the dashboard

New owners used to land on blank tables with no guidance about what to do next. Four dashboard surfaces got proper empty states:

• /dashboard/bots — "Create your first bot" card with a link to the wizard
• Conversations tab — "No conversations yet" with context about when threads appear; search-with-no-results now says "No threads matched X" with a Clear-search action instead of falsely claiming "no conversations yet"
• Sources page — Three kind-tinted chips (URL / PDF / Text) that deep-link straight into the right add-form tab
• Analytics tab — "No data yet" with an explanation of the 24-hour warm-up period

Each empty state has exactly one next-step CTA — no stacked hint paragraphs, no walls of text.

Commit: eff7619