Add copy to clipboard button for sessions

[Reasel]

Summary

• Adds a clipboard icon next to the delete icon on each session history row
• Clicking it copies session stats to the clipboard in a readable format:

  Session: My AFK Session
  Length: 15m 32s
  Consistency: 85
  Avg Interval: 1200ms
  Clicks: 47
  

• Session length is calculated from start/end timestamps and formatted as hours/minutes/seconds
• Adds hover highlight effect with rounded corners on session icon buttons
• Adds visual indicator bars below the Consistency and Avg Click Interval stats
  • Consistency: linear scale 0-100 with tick marks every 10
  • Avg Click Interval: logarithmic scale 0-150s with tick marks at key intervals
  • Both use an orange triangle marker to show the current value

Test plan

• Start and complete a session, verify clipboard icon appears in the history row
• Click the clipboard icon and paste — verify the format includes session name, length, consistency, avg interval, and click count
• Verify duration formatting: seconds-only, minutes+seconds, and hours+minutes+seconds
• Verify consistency indicator shows marker at correct position on 0-100 scale
• Verify click interval indicator shows marker at correct position on logarithmic 0-150s scale
• Hover over indicators and verify tooltip text appears