docs: remove unnecessary --save flag in npm install command

[lipperhey]

What changed? Why?
The --save flag in npm install is no longer necessary since modern versions of npm save dependencies by default. Removed it to keep the command cleaner and up to date.

Notes to reviewers
This is a small cleanup to align with current npm behavior. No functional changes.

How has it been tested?
Manually verified that npm install without --save still correctly adds dependencies to package.json.

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

BaseDocs

• docs.base.org
• docs sub-pages

[vercel]

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

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[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 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 0 Sum 1