fix(company): add dashboard greeting fallback

[szx19970521]

Summary

Adds a company dashboard greeting fallback so fresh Privy signups without a company name render Welcome back, there instead of exposing an undefined value.

Acceptance criteria

• No "Hello, undefined" / undefined greeting string on a fresh signup.
• If the name is set, the existing greeting is preserved.

Closes #70

[vercel]

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