docs: update CHANGELOG with Phase 0 documentation

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

CHANGELOG.md

@@ -14,3 +14,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Build-time version generation from pubspec.yaml (`dart run tool/generate_version.dart`)
 - Version logging on app startup
 - Project documentation (PHILOSOPHY.md, README.md, AGENTS.md, PLAN.md)
+- Phase 0 technical documentation:
+  - docs/ARCHITECTURE.md - Clean Architecture patterns
+  - docs/API_INTEGRATION.md - Backend API reference
+  - docs/DEPLOYMENT.md - Docker and infrastructure setup
+  - docs/DATAGRID.md - DataGrid component specification
+  - docs/THEMING.md - Material 3 theming guide