Drop the loading spinner on the Me and Projects sidebar links

Clicking Me or Projects in the sidebar swaps the link's icon for a spinner until the panel arrives. Both panels load fast enough that the spinner only flickers and adds noise. The icon should stay put; the link should still turn active straight away, as it does now.

Where

• internal/server/templates/shell_sidebar.html: the data-nav-loader spans inside the Me and Projects links (the only two links that have one).
• internal/server/static/app.js: setNavLoading, called from the htmx:beforeRequest / htmx:afterRequest handlers for [data-sidebar-link].

Keep The top-of-page .nav-progress bar (driven by data-nav-busy / syncNavBusy). It only appears after a 150 ms delay, so it stays hidden on fast loads and still covers a slow one.

Done when

• Clicking Me or Projects shows no spinner. The icon never changes, and the active state still moves immediately.
• The loader markup and setNavLoading are gone, provided nothing else uses them.
• If the Tailwind output changes, app.css is rebuilt (npm run assets).