fix(cli): support Volta auto updates

[pragnyanramtha]

Summary

Fixes the auto-updater loop for Gemini CLI installations managed by Volta by detecting Volta-managed executable paths and using Volta's install command instead of falling back to npm.

Details

• Adds PackageManager.VOLTA to installation detection.
• Detects Volta from VOLTA_HOME as well as common .volta, volta/bin, and volta/tools paths.
• Returns volta install @google/gemini-cli@latest for global Volta installs.
• Keeps standalone binary detection ahead of path-based package manager detection.

Related Issues

Fixes #26573

How to Validate

• npm run test --workspace packages/cli -- installationInfo.test.ts
  • Expected: src/utils/installationInfo.test.ts passes 20/20 tests and the package posttest build completes.
• git diff --check origin/main...HEAD

Note: an initial attempt with --runInBand was rejected because Vitest does not support that Jest flag; the command above is the successful validation run.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any): none
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

Windows validation is covered by the VOLTA_HOME Windows-path unit test; Linux/macOS-style validation is covered by the .volta/tools path unit test.

[pragnyanramtha]

Closing this draft because the branch was accidentally published from the Reputation-DAO organization fork. Replacement from my personal fork: #27103