Display bundle size numbers with commas in absolute bytes

[Copilot]

This PR improves the UI by displaying bundle size numbers as absolute values with comma separators instead of abbreviated KB values.

Changes Made

Before: Bundle sizes were displayed as rounded KB values (e.g., "555KB")
After: Bundle sizes are now displayed as absolute byte values with commas (e.g., "568,609 bytes")

Key Updates:

1. Data Format: Changed bundleSizeData to use actual byte values (stat.totalSize) instead of converting to KB
2. Number Formatting: Added formatNumberWithCommas() utility function using toLocaleString() for proper comma formatting
3. Chart Labels: Updated from "Bundle Size (KB)" to "Bundle Size (bytes)" in chart legend
4. Stat Card: "Latest Bundle Size" now shows formatted bytes (e.g., "568,609 bytes")
5. Tooltips: Added custom formatter for bundle size chart tooltips to display numbers with commas

Visual Impact:

• Y-axis now shows appropriate scale (0, 150000, 300000, 450000, 600000)
• Stat cards display precise byte counts with thousands separators
• Chart tooltips show formatted numbers for better readability
• Other charts (Build Time, File Types) remain unchanged

The implementation uses minimal code changes while preserving all existing functionality and maintaining the responsive design.

Fixes #24.

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