feat: Add /stats command for token usage statistics #10240

Description

Currently there's no easy way to view token usage statistics and activity history in OpenCode. Users have to manually calculate their usage or check external dashboards.

Proposed Solution

Add a /stats slash command that opens a dialog showing:

1. Activity Heatmap - GitHub-style contribution graph showing daily token usage intensity

   • 3 view modes: 7 days, 30 days, 1 year (toggle with Shift+R)

2. Token Summaries - Side-by-side comparison of 7-day and 30-day stats

   • Input/Output/Cache tokens
   • Session count
   • Cost estimate

3. Model Usage Breakdown - Visual bar charts showing token distribution by model

Benefits

• Quick visibility into usage patterns
• Helps users understand their token consumption
• Identifies which models are being used most
• Provides cost awareness

Related

• PR Separate context window and session stats in sidebar #6313 - Separate context window and session stats in sidebar
• PR feat: display Google Gemini cached token stats #6860 - Display Google Gemini cached token stats

This feature provides a more comprehensive, dedicated view for statistics rather than sidebar-based stats.