update changelog with sequential migration system

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 ## [Unreleased]
 
 ### Added
+- Sequential migration system (`migrations/migrate.py`) — tracks applied versions in `_migrations` table, auto-detects fresh vs existing DBs, runs pending migrations in order
+- `migrations/versions/0001_rename_ls_to_paddle.py` — first versioned migration (absorbed from `scripts/migrate_to_paddle.py`)
 - Server-side financial calculator (`planner/calculator.py`) — ported JS `calc()`, `pmt()`, `calcIRR()` to Python so the full financial model is no longer exposed in client-side JavaScript
 - `POST /planner/calculate` endpoint for server-side computation
 - Pre-computed initial data (`window.__PADELNOMICS_INITIAL_D__`) injected on page load for instant first render
@@ -26,6 +28,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   - Zero-downtime: new slot health-checked before traffic switch
   - Automatic rollback on failed health check
 
+### Removed
+- `scripts/migrate_to_paddle.py` — superseded by `versions/0001_rename_ls_to_paddle.py`
+
 ### Changed
 - `planner.js` no longer contains `calc()`, `pmt()`, or `calcIRR()` functions — computation moved server-side
 - `render()` split into `render()` (tab switching + schedule calc) and `renderWith(d)` (DOM updates from data)