Update timezones page with UI settings and query timezone hierarchy

[mintlify]

Summary

• Added the new query timezone hierarchy: per-chart → UI settings → env var → UTC
• Documented the new project query timezone UI setting for admins in Settings > Project Settings
• Updated the per-chart timezone picker section (now available in the Explore view)
• Updated workarounds and summary table to reference the new options
• Reordered sections to reflect the priority hierarchy

[github-actions]

🤖 Documentation Bot

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