feat(users): add create/update methods

[noticeeverything]

Note

Introduces user create/update capabilities and tightens typings while aligning CI/runtime to Node 24.

• Adds Users.create(data) and Users.update(id, data) to src/lib/graph-api/users/users.ts, handling optional manager (validates, assigns via assignManager, removes via removeManager, and skips if unchanged)
• Extends typings: fixes GraphUser boolean fields (accountEnabled, onPremisesSyncEnabled, showInAddressList) and adds CreateOrUpdateGraphUser (omits password/readonly fields; optional manager?: string | null)
• Adds tests in users.spec.ts covering create/update flows including manager presence, change, removal, and no-op scenarios
• CI/runtime: pin Node to 24 in .github/workflows/* and update Volta node to 24.12.0 in package.json

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