Windows classroom install: NSIS installer and admin checklist

[Hmbown]

Problem

Manual Windows install is workable for technical users, but teachers, lab admins, and stubborn classroom environments need a boring installer path. The current advice requires users to place both binaries side-by-side and manage PATH themselves.

Scope

For v0.8.44, add a narrow Windows install track rather than a broad updater/release rewrite.

• Add an NSIS installer path for the released Windows assets.
• Install both codewhale.exe and codewhale-tui.exe side-by-side.
• Default to a per-user install under %LOCALAPPDATA%\Programs\CodeWhale\bin.
• Add the install directory to the current user's PATH.
• Include an uninstaller that removes the PATH entry cleanly.
• Document the manual fallback for users who avoid unsigned installers or hit SmartScreen.
• Add a classroom/admin checklist: install, PATH check, codewhale --version, codewhale-tui --version, codewhale doctor, config reset, and first-run smoke test.

Non-goals

• No auto-updater in the first installer PR.
• No telemetry, hosted services, or bundled third-party tools.
• No signing/notarization claims unless signing is actually configured.

Acceptance criteria

• A Windows user can install both binaries without understanding the dispatcher/TUI split.
• The installer can be built reproducibly from release artifacts or documented local inputs.
• Uninstall removes files and PATH changes cleanly.
• Docs clearly describe manual install, installer install, and the two-binary requirement.

Related: #1561
Related tracker: #1878