v1.3.0

Add heap dump diff view for memory growth analysis

Implements interactive comparison of two heap dumps to identify memory
leaks and growth patterns. Users can select any 2 dumps via checkboxes
and view allocation deltas in an interactive pprof interface.

Features:
- Multi-select UI with checkboxes on each dump row
- Floating 'Compare Selected (2)' button appears when 2 dumps selected
- Automatic chronological ordering (older dump as base)
- New /pprof-diff/{base}/{compare}/ endpoint
- Extended pprof server to support diff mode using -base flag
- Visual feedback with blue highlighting on selected rows
- Interactive diff view shows growing/shrinking functions
- Updated documentation and API reference

The diff view leverages pprof's built-in comparison capability to show:
- Allocation deltas (positive/negative changes)
- Growing functions highlighted in red
- Shrinking allocations in green
- Flamegraphs focused on growth areas
- Top allocations ranked by delta

This is a critical debugging workflow that makes identifying leak sources
significantly faster by comparing memory states over time.

Documentation:
- Updated ROADMAP.md to mark feature as completed
- Updated CLAUDE.md with detailed implementation guide
- README.md already includes usage instructions and API reference

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>