feat(css): co-locate block CSS with auto-discovery via Tailwind pipeline

Move block-specific CSS from centralized assets/css/blox/ to co-located
style.css files within each block directory. The css.html partial now
auto-discovers style.css files from bundled and community blocks and
concatenates them into the Tailwind entry via resources.Concat, enabling
full @apply support while avoiding VFS path resolution issues.

Shared biography styles (avatar, ruby) are extracted to blox/shared/css/
and auto-included before per-block styles. Navbar CSS moves to
components/ as it's a framework-level concern. The separate community
CSS pipeline in site_head.html is removed — all block CSS now flows
through a single Tailwind entry point.

modules/blox/assets/css/main.css

@@ -34,8 +34,10 @@
 
 /* Hugo Blox module components */
 @import "components/all.css";
-@import "blox/all.css";
 @import "views/all.css";
+
+/* Block-specific CSS is auto-discovered from co-located style.css files */
+/* See css.html partial for the discovery mechanism */
 @import "chroma.css";
 
 /* Hugo Blox Search */