Fix dashboard XSS and silent error handling

[CalebisGross]

Summary

• Dashboard chat panel uses innerHTML without consistent sanitization (XSS) #4: Sanitize all innerHTML insertions that used raw server/LLM data without escapeHtml() — episode badges, pattern/abstraction state badges, graph tooltips, detail panel metadata, and connection type labels
• Empty catch blocks silently swallow errors in dashboard #5: Replace empty catch blocks with console.error logging and user-visible toast notifications for graph loading, insights loading, and WebSocket parse failures

Closes #4, closes #5

Test plan

• Open dashboard, verify episodes/patterns/abstractions render correctly
• Hover graph nodes — tooltip should display escaped content
• Click a graph node — detail panel meta and connections should render safely
• Stop the mnemonic server, reload dashboard — verify error toasts appear for failed loads
• Check browser console for logged errors instead of silent swallowing

🤖 Generated with Claude Code