feat(core,tooling): Windows support — shell selection, install.ps1, win-x64 release package, Windows CI (#79)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -101,7 +101,7 @@ Each family's latest generation only — the app's **Models** page lists every b
 
 | Requirement  | Supported                                                                  |
 | ------------ | -------------------------------------------------------------------------- |
-| OS           | Linux, macOS                                                               |
+| OS           | Linux, macOS, Windows 10+                                                  |
 | Architecture | x64, arm64                                                                 |
 | Runtime      | bundled by the one-line installer (npm installs need Node >= 24)           |
 | Model        | an API key for at least one model                                          |
@@ -117,6 +117,8 @@ curl -fsSL https://penguin.ooo/install.sh | sh
 penguin web        # start the service and open http://127.0.0.1:7364 (first login: admin / penguin-2026)
 ```
 
+🪟 On Windows (PowerShell): `irm https://penguin.ooo/install.ps1 | iex`
+
 📦 Or via npm: `npm install -g @prismshadow/penguin-cli`. Configure models on the in-app Models page, then chat.
 
 ### 🤖 CLI & SDK — for agents
@@ -149,7 +151,7 @@ for await (const output of session.run([userText("Create hello.txt containing hi
 
 - [ ] Public release of the benchmark suite
 - [ ] Desktop app
-- [ ] Windows support
+- [x] Windows support
 - [ ] Agent company and templates
 - [ ] Company-level self evolving
 - [ ] OpenShell integration (permission-governed shell)