feat(install): support Windows PowerShell installs

[Mineru98]

Context

Closes #39.

Windows users only had the Unix install.sh path, which assumes Bash, tar/chmod, Unix release archives, and direct escript execution. Issue #39 asks for a Windows-native PowerShell install/launch path while preserving the existing macOS/Linux flow.

What Changed

• Added install.ps1 for Windows release zip installs into %LOCALAPPDATA%\Ourocode\<version> with SHA256 verification, prerequisite guidance for Erlang/OTP, and User PATH registration without setx.
• Added uninstall.ps1 so Windows installs can be removed and reinstalled repeatedly; broad system/profile roots are rejected before recursive deletion.
• Added scripts/package-windows.ps1 and a Windows package CI smoke workflow.
• Added Windows .cmd / .ps1 launchers that invoke escript.exe <script> and set OUROCODE_TTY when the helper exists.
• Split ourocode_tty by platform and implemented a Windows console helper using windows-sys, while keeping the existing Unix termios path under cfg(unix).
• Added a Linux/macOS regression workflow so Unix helper build/package paths stay covered.
• Updated README and docs site with Windows install, uninstall/reinstall, prerequisite, checksum, and release-builder guidance.

Verification

• cargo build --release --manifest-path rust\ourocode_ipc\Cargo.toml --bin ourocode_tty
• cargo test --manifest-path rust\ourocode_ipc\Cargo.toml
• mix test test/ourocode/terminal/tty_driver_test.exs
• git diff --check
• Real Windows install from dist\ourocode-v0.1.14-tui-windows-x64.zip into %LOCALAPPDATA%\Ourocode\0.1.14-tui
• Fresh PowerShell/cmd lookup of ourocode.cmd
• ourocode --smoke-test
• Interactive Windows TUI smoke: ourocode, /commands, /exit

Notes

• This keeps Erlang/OTP as a prerequisite instead of bundling it.
• Local LSP diagnostics could not run because rust-analyzer.exe is missing from the installed Rust toolchain, but cargo build/test passed.
• The existing .gitignore local edit is intentionally not part of this PR.