Update CHANGELOG.md for version 1.5.0

CHANGELOG.md

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+# Changelog
+
+## 1.5.0 - 2025-12-29
+
+### Features
+
+- Move to IndexedDB for saving graph data (from localStorage)
+- Add multiple links support between nodes.
+- Increase undo/redo history to 100 steps.
+- Move undo/redo operations to IndexedDB instead of memory.
+- Mass selection improvements (moving and linking multiple nodes at once).
+- Codebase refactor to use Svelte 5 Runes.
+- Mobile improvements
+
+### Dependency Updates
+
+- `@sveltejs/kit`: ^2.49.1 -> ^2.49.2
+- `@typescript-eslint/eslint-plugin`: ^8.50.1 -> ^8.51.0
+- `@typescript-eslint/parser`: ^8.50.1 -> ^8.51.0
+- `svelte`: ^5.45.6 -> ^5.46.1
+- `svelte-check`: ^4.3.4 -> ^4.3.5
+- `vite`: ^7.2.6 -> ^7.3.0
+
+### Major Codebase Changes
+
+- Moved from `npm` to `pnpm`
+- Updated license from `MIT` to `BSD-3-Clause`
+- Moved from `Makefile` to `Taskfile`
+- Codebase organization and structure changes