chore: replace deprecated inputValidator with validator

[igboyes]

Summary

• TanStack Start deprecated createServerFn().inputValidator() in favor of .validator(); this updates all remaining call sites so we're not building against a removed API.
• Renames inputValidator to validator across auth, groups, jobs, labels, messages, tasks, and users server functions.
• No behavior change — schemas and handlers are untouched.

[linear-code]

VIR-2610

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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