Don't explicitly set perf tier, it's plan dependent

[ivpusic]

Unless explicitly provided, perf tier will be auto selected for the used

[cursor]

PR Summary

Medium Risk
Behavior change for CLI executions that previously implicitly used medium performance; may affect users/scripts relying on the old default or the removed small tier.

Overview
query run and query run-sql no longer default --performance to medium; the flag now defaults to empty so the API can auto-select the appropriate tier unless the user explicitly sets one.

Validation and help text were updated accordingly (dropping support for small and clarifying override semantics), and new tests assert that omitted --performance results in an empty Performance field being sent.

^{Reviewed by Cursor Bugbot for commit 41c7c2f. Configure here.}

[charisra]

bugbot run

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 41c7c2f. Configure here.}