Change mansion tax map to show % of local properties affected

Instead of showing what share of Scotland's £1m+ properties are in each
constituency, now shows what percentage of properties within each
constituency are valued over £1m.

- Added estimated_dwellings and pct_local_affected columns to CSV
- Used NRS dwelling data scaled to 2024 (2.74M total dwellings)
- Updated map color scale (0-0.11% range)
- Updated title, description, tooltip, and search results

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

Author: MaxGhenis