fix(next-config): guard BLOB_STORE_ID in images.remotePatterns

[aldoprogrammer]

Fix Next.js crash when BLOB_STORE_ID is missing

Summary

Fixes a Next.js startup crash caused by an invalid images.remotePatterns entry
when BLOB_STORE_ID is not defined.

Context

On a clean setup, next.config.js always added an image remote pattern using
process.env.BLOB_STORE_ID, resulting in an invalid hostname and causing
Next.js strict config validation to fail.

This issue was previously reported in #417,
where the suggested workaround was to manually define a dummy BLOB_STORE_ID.

Changes

• Conditionally include the BLOB_STORE_ID image host only when the env variable is defined
• Prevents invalid remotePatterns entries on fresh installs

Testing

• pnpm dev without BLOB_STORE_ID
• pnpm dev with BLOB_STORE_ID set
• pnpm build

Related

• Fixes #490
• Related: #417