Add Export/Import Lap Data Feature

Users should be able to export their lap times to CSV/JSON for analysis and import previously saved sessions. This would be valuable for athletes, productivity tracking, and data analysis.

Features to implement:

Export button that downloads lap data as CSV
Export button that downloads lap data as JSON
Import functionality to load previously exported sessions
Display export/import options in a clean modal or dropdown
Technical Details:

CSV format: Lap Number,Time,Difference
JSON format: Array of lap objects with timestamp, duration, difference
Include session metadata (date, total time, etc.)
Validate imported data format
Files to modify:

[script.js](vscode-file://vscode-app/c:/Users/Gupta/AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/code/electron-browser/workbench/workbench.html) - Add export/import functions
[index.html](vscode-file://vscode-app/c:/Users/Gupta/AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/code/electron-browser/workbench/workbench.html) - Add export/import buttons
[style.css](vscode-file://vscode-app/c:/Users/Gupta/AppData/Local/Programs/Microsoft%20VS%20Code/resources/app/out/vs/code/electron-browser/workbench/workbench.html) - Style the export/import UI