@github/copilot@prerelease installs, but copilot --version and copilot update still report 1.0.11

Title: @github/copilot@prerelease installs, but copilot --version and copilot update still report 1.0.11

Body:

I’m seeing a mismatch between the prerelease npm tag and the installed CLI version on Windows.

Steps I took
Removed the winget package:
winget uninstall GitHub.Copilot.Prerelease
Installed npm prerelease:
npm install -g @github/copilot@prerelease --force
Verified installed package:
npm list -g --depth=0 @github/copilot
Verified the CLI:
copilot --version
copilot update
Removed the VS Code Copilot CLI shim so it would not shadow the npm binary.
Actual results
Installed npm package: @github/copilot@1.0.12-2
copilot --version returns: GitHub Copilot CLI 1.0.11
copilot update returns:
No update needed, current version is 1.0.11, fetched latest release is v1.0.11
Expected results
Installing @github/copilot@prerelease should produce a CLI that reports the prerelease version, or copilot update should target the prerelease channel.
Environment
Windows
PowerShell
npm prerelease tag:
latest: 1.0.11
prerelease: 1.0.12-2
Notes
I confirmed this is not a PATH/shim issue:

winget package was removed
VS Code Copilot CLI shim was removed
the npm binary is the one being executed
the CLI still reports 1.0.11

Made bug Copilot :)

Reproduce the issue in PowerShell with `npm install -g @github/copilot@prerelease --force`, then run `copilot --version` and `copilot update`. Trace the version-reporting and update entry points to find why package 1.0.12-2 resolves to 1.0.11; done means the prerelease version is reported and update behavior matches the expected channel.

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