Add architecture diagram to landing page #1

Proposal

Add the jss-architecture.svg diagram (from the main JSS repo) to the landing page to give visitors a visual overview of how the pieces fit together.

Placement

New "Architecture" section between the "Why JSS?" feature grid and the "Get Started" CTA.

Approach

• Copy jss-architecture.svg into this repo (keeps landing page self-contained, no hotlink dependency)
• Add a new <section class="architecture"> with the SVG centered and responsively sized
• Match existing visual style (light background like .cta, consistent padding)

Rationale

The feature list enumerates capabilities but doesn't show how LDP, Solid-OIDC, Git, Nostr, remoteStorage, etc. relate. A diagram closes that gap for visitors evaluating the server.