fix(engine): robust Windows install + ship rocky-lsp alongside rocky

[hugocorreia90]

The bug

Running the Windows install one-liner while VS Code is open fails:

Copy-Item: The process cannot access the file
'C:\Users\…\AppData\Local\rocky\bin\rocky.exe' because it is being used by another process.

Why

Two things combine:

1. install.ps1 overwrote rocky.exe in place with Copy-Item -Force. On Windows a running executable is locked, so the overwrite fails.
2. Neither installer ships the standalone rocky-lsp. The VS Code extension prefers rocky-lsp for the language server but, not finding it, falls back to spawning rocky lsp — so it runs rocky.exe, locking the exact file the installer is replacing.

install.sh (macOS/Linux) didn't hit this because it uses mv (atomic rename, fine over a running binary on Unix). This was Windows-only.

The fix (two complementary changes)

1. Rename-then-replace on Windows. Renaming an in-use binary is allowed on Windows (the running process keeps its handle), so install.ps1 now mirrors install.sh's mv: try a normal copy, and on a locked overwrite move the old binary aside (rocky.exe.old-<rand>) and drop the new one in. Stale .old files are swept on the next run. The install now succeeds while VS Code is open.

2. Ship rocky-lsp alongside rocky (both installers). This removes the root cause: when rocky-lsp is present the extension uses it for the LSP and never runs rocky.exe, so rocky.exe is never locked. Both installers best-effort download rocky-lsp-<target>, verify it against the same checksums.txt, and place it with the same mechanism as rocky. The Windows rename-replace is factored into an Install-RockyBinary helper so both binaries get identical robust install (and rocky-lsp's own future updates are covered too).

Best-effort and non-fatal: if the rocky-lsp archive is missing (older release) or fails verification, it's skipped and the extension falls back to rocky lsp. The core rocky install is unchanged.

No release needed — the one-liners fetch the scripts from main, so this takes effect on merge.

Verification

• bash -n + shellcheck -S error clean on install.sh.
• install.ps1 hand-verified (no pwsh on the build host): -ErrorAction Stop makes the lock error terminating so the catch fires; non-lock failures rethrow; the unique .old-<rand> name avoids colliding with a still-locked prior .old; Install-RockyBinary is defined before its call sites; the rocky-lsp block reuses the already-fetched checksums.txt and is wrapped so any failure is non-fatal.

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