Add v0.4.2 release notes

docs/releases/v0.4.2.md

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+## Cassady v0.4.2
+
+Cassady v0.4.2 brings full slash-command support to the desktop app and moves command parsing/execution into a shared core so the terminal UI and desktop app stay in sync.
+
+### Downloads
+
+- macOS Apple Silicon: `cassady-v0.4.2-aarch64-apple-darwin.tar.gz`
+- Linux x86_64: `cassady-v0.4.2-x86_64-unknown-linux-gnu.tar.gz`
+- Linux ARM64: `cassady-v0.4.2-aarch64-unknown-linux-gnu.tar.gz`
+- Windows x86_64: `cassady-v0.4.2-x86_64-pc-windows-gnu.zip`
+
+The macOS and Linux archives contain `cass`, `cassady`, and `cassady-desktop`; launch the desktop app with `cass desktop`. The Windows archive contains `cass` and `cassady`. SHA-256 checksum files are included for every archive.
+
+### Highlights
+
+- Adds a filterable desktop slash-command menu with keyboard navigation, grouped autocomplete, click-outside dismissal, and auto-run for complete command selections.
+- Supports desktop execution for `/fast`, `/status`, `/model`, `/new`, and `/resume`, including status blocks, footer updates, transcript rebuilds, and resume warnings.
+- Adds native desktop modals for `/login`, `/logout`, and `/branch`/`/restore`, covering provider setup, provider removal, branch switching, checkpoint branching, and optional tracked-file restore.
+- Moves the command catalog, parser, autocomplete, and pure command actions into the shared `cassady::commands` module so CLI and desktop behavior use the same implementation.
+- Expands the embedding/session surface used by the desktop app with config/conversation accessors and shared model-selection logic.
+
+### Upgrade notes
+
+No config migration is required. Desktop users should update both `cass` and the companion `cassady-desktop` binary from the same v0.4.2 macOS/Linux archive so the new slash-command frontend and Tauri commands match.
+
+### Install from source
+
+```sh
+cargo install --git https://github.com/owenqwenstarsky/cassady --tag v0.4.2
+```
+
+### Verification
+
+Built and tested with the GitHub Actions release workflow:
+
+```sh
+cargo test --locked --all-targets
+cargo build -p cassady --release --locked --target aarch64-apple-darwin --bin cass --bin cassady
+(cd cassady-desktop && cargo tauri build --target aarch64-apple-darwin --no-bundle -- --locked)
+cargo build -p cassady --release --locked --target x86_64-unknown-linux-gnu --bin cass --bin cassady
+(cd cassady-desktop && cargo tauri build --target x86_64-unknown-linux-gnu --no-bundle -- --locked)
+cargo build -p cassady --release --locked --target aarch64-unknown-linux-gnu --bin cass --bin cassady
+(cd cassady-desktop && cargo tauri build --target aarch64-unknown-linux-gnu --no-bundle -- --locked)
+cargo zigbuild -p cassady --release --locked --target x86_64-pc-windows-gnu --bin cass --bin cassady
+```