Fix basename domain fallback to avoid double-dot domains

[kinderjoypresents]

What changed? Why?

• Use base.eth (no leading dot) as the fallback domain when chainId is not present in USERNAME_DOMAINS.

Notes to reviewers

• The previous fallback used a leading dot, which could generate an invalid/incorrect basename string with a double dot and potentialy break ENS formatting.

How has it been tested?

• Manual review (string output formatting) for known chainIds and unknown chainIds."

Have you tested the following pages?

BaseWeb

• [] base.org
• [] base.org/names
• [] base.org/builders
• [] base.org/ecosystem
• [] base.org/name/jesse
• [] base.org/manage-names
• [] base.org/resources

[vercel]

@kinderjoypresents is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2