chore: remove deprecated flow_boundary and update docs to match new architecture

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+### Changed
+
+### Deprecated
+
+- `FlowSource` struct - Use `RefrigerantSource`, `BrineSource`, or `AirSource` instead
+- `FlowSink` struct - Use `RefrigerantSink`, `BrineSink`, or `AirSink` instead
+- `FlowSource::incompressible()` - Use `BrineSource::new()` instead
+- `FlowSource::compressible()` - Use `RefrigerantSource::new()` instead
+- `FlowSink::incompressible()` - Use `BrineSink::new()` instead
+- `FlowSink::compressible()` - Use `RefrigerantSink::new()` instead
+- Type aliases `IncompressibleSource`, `CompressibleSource`, `IncompressibleSink`, `CompressibleSink` - Use typed alternatives instead
+
+### Removed
+
+### Fixed
+
+### Security
+
+## [0.2.0] - 2026-02-24
+
+### Added
+
+- **Epic 10: Enhanced Boundary Conditions**
+  - `RefrigerantSource` and `RefrigerantSink` for refrigerant circuits with native vapor quality support
+  - `BrineSource` and `BrineSink` for liquid heat transfer fluids with glycol concentration support
+  - `AirSource` and `AirSink` for humid air with psychrometric property support
+  - New physical types: `VaporQuality`, `Concentration`, `RelativeHumidity`, `WetBulbTemperature`
+
+### Changed
+
+### Deprecated
+
+- `FlowSource` and `FlowSink` - See migration guide at `docs/migration/boundary-conditions.md`
+
+### Fixed
+
+## [0.1.0] - 2024-12-01
+
+### Added
+
+- Initial release with core component framework
+- `FlowSource` and `FlowSink` boundary conditions
+- Basic solver infrastructure
+- Python bindings via PyO3