Add Merch link to header

[gerth2]

Description

added a merch store link

Meta

Merge checklist:

• [x ] Pull Request title is short, imperative summary of proposed changes
• The description documents the what and why
• If this PR changes behavior or adds a feature, user documentation is updated
• If this PR touches photon-serde, all messages have been regenerated and hashes have not changed unexpectedly
• If this PR touches configuration, this is backwards compatible with settings back to v2025.3.2
• If this PR touches pipeline settings or anything related to data exchange, the frontend typing is updated
• If this PR addresses a bug, a regression test for it is added

[Gold856]

It's weird that "All Products" isn't actually all the products sold.

[samfreund]

• [x ] Pull Request title is short, imperative summary of proposed changes

BTW, you don't put any spaces, so it's just [x]

LGTM tho