UX Improvements: Enhance Team Creation Navigation

[satococoa]

Add "+ Create Team" option in team switcher dropdown (similar to Vercel's pattern)

Warning

You will face these issue, if you use shadcn/ui Select & Dialog.

• Dialog and Input strange behaviour - input value overwrite shadcn-ui/ui#2487
• Dialog & DropdownMenu adds pointer-events: none; shadcn-ui/ui#1859
• [Dialog] body pointer-events: none remains after closing radix-ui/primitives#1241

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I’m planning the following options for the "Create Team" button, but I think it would be best to address this as part of a broader UX improvement effort later:

• Include both an 👤 icon and text like "Create Team" to make the button's purpose clearer.
• Add a "+ Create Team" link to the team switcher dropdown, similar to Vercel.

Originally posted by @shige in #163 (review)