Support Windows as a first-class platform

[setkyar]

pi-web builds a windows/amd64 binary but Windows isn't actually supported: state-file locking is a no-op, self-update restart errors out, and the npm postinstall (bash install.sh) fails outright on Windows, so there's no install or auto-start story.

The pi CLI itself supports Windows natively (see pi's docs/windows.md; Git Bash is the only prerequisite), so the remaining work is all on pi-web's side:

• State-file locking via LockFileEx (feat(windows): real state-file locking, self-update restart, Windows CI #95)
• Self-update restart support (feat(windows): real state-file locking, self-update restart, Windows CI #95)
• Windows installer + uninstaller with admin-free auto-start on login (feat(windows): PowerShell installer, Run-key auto-start, extension + docs #97)
• /web auto-start and /pi-web start|stop|restart extension support on win32 (feat(windows): PowerShell installer, Run-key auto-start, extension + docs #97)
• Windows CI job — go test / go vet on windows-latest, plus PowerShell parse-check (feat(windows): real state-file locking, self-update restart, Windows CI #95, feat(windows): PowerShell installer, Run-key auto-start, extension + docs #97; the first run surfaced 36 Unix-assuming test failures and two real product bugs in project-name encoding, fixed in feat(windows): real state-file locking, self-update restart, Windows CI #95)
• windows/arm64 release binaries (feat(windows): real state-file locking, self-update restart, Windows CI #95)
• English docs: README badge, install guide, auto-start section (feat(windows): PowerShell installer, Run-key auto-start, extension + docs #97)
• Regenerate the 13 translations (scripts/build_readmes.py + scripts/build_userdocs.py) now that the English text is merged
• Smoke test on a real Windows machine: pi --mode rpc through the npm pi.cmd shim, installer end-to-end (pi install npm:@ygncode/pi-web@beta), login auto-start, in-app update + restart