style(web): main sidebar drops 16rem to 14rem (user review)

The app-shell sidebar read as too wide against the content area.
--sidebar-w is the single source of truth for the shell geometry, so
one line moves all three consumers together: the .app-sidebar width,
the body:has(.app-sidebar) content offset, and the topbar's left
inset on desktop. No templ or JS change needed — nothing else pinned
16rem.

style.css is the regenerated tailwind build (build:css:prod), diff
limited to the one var; committed with its source per the generated-
artifacts rule.

web/static/input.css

@@ -486,7 +486,7 @@
    * which Alpine flips through `mobileMenuOpen`) and pinned on >= lg.
    */
   :root {
-    --sidebar-w: 16rem;
+    --sidebar-w: 14rem;
     --topbar-h: 4rem;
   }