feat: Shareable session dashboard export

[sagarsrc]

Summary

Add ability to export and share a session as a standalone, responsive dashboard that can be viewed without running supertrace.

Problem

Currently, session data is only viewable within the supertrace app. Users can't easily share session analytics with teammates, stakeholders, or for documentation purposes.

Proposed Solution

Add a share/export feature accessible via a 3-dot menu on each session in the sidebar.

UX Flow

1. User clicks 3-dot menu (⋮) on a session in the sidebar
2. Menu shows "Share" option
3. Clicking "Share" generates an exportable dashboard

Implementation

Frontend - Sidebar Menu:

• Add 3-dot menu (⋮) button on session items in sidebar
• Menu options: "Share", "Delete", "Copy Session ID"
• Share option opens export modal/dialog

Frontend - Export Options:

• Export as standalone HTML file (self-contained, no server needed)
• Export as PNG/image (for quick sharing)
• Copy shareable link (if hosted sharing is implemented later)

Frontend - Exported Dashboard:

• Fully responsive (mobile, tablet, desktop)
• Self-contained HTML with embedded CSS/JS
• Includes key metrics: tokens, cost, duration, tool usage
• Shows conversation flow/timeline
• Analytics charts (token usage over time, tool distribution)
• Dark/light mode support
• Supertrace branding/watermark

Backend:

• Endpoint GET /api/sessions/{session_id}/export returns exportable data
• Option to generate static HTML server-side

Visual Example

Sessions
├── quickcall-supertrace  [⋮]
│                          ├── Share
│                          ├── Copy Session ID  
│                          └── Delete
├── my-project
└── another-session

Exported Dashboard Contents

• Session metadata (project, date, duration)
• Summary metrics (tokens, cost, cache savings)
• Tool usage breakdown
• Timeline/conversation overview
• Charts (optional, can be simplified for export)

Benefits

• Share session insights with team members
• Document AI usage for reports/reviews
• No need to grant supertrace access to viewers
• Offline viewing capability

Additional Context

• Similar to how observability tools export traces/dashboards
• HTML export should work offline (no external dependencies)
• Consider file size optimization for large sessions