feat: Added Unified file system / default layout mounts.

TODOS.md

@@ -1,10 +1,12 @@
 - README.md
   - [ ] "Zero is beautiful"
 - [ ] Content-hash fingerprinting for CSS and JS cache busting
+- [ ] Clean up the default layouts
 - [ ] Performance
   - [ ] See if we can disable bounds checks in `write_indented` and elsewhere.
   - [ ] Instead of loading the site fresh each time in watch mode, create a
         `reload_site` proc, that just updates changed resources.
+  - [ ] Only publish referenced assets.
 - [ ] mustache data keys for opengraph, etc.
 - [ ] Block attributes on code fences (`{ #ex-1 }`) — hello-world.md
 - [ ] include-code shortcode (`{{< include-code ... >}}`) — i-ported-fd-to-odin
@@ -35,6 +37,7 @@
 - [ ] Free cmark HTML output (`body_html`) — cmark allocates via C malloc, not the arena, so it leaks per iteration in watch mode
 - [ ] Rename `{{#is_post}}` to `{{#is_article}}` in templates and data model — currently hardcoded to posts section, should use `is_article` (any page with a section) instead.
 - [ ] Split `load_page` into frontmatter-parse + body-process phases so draft pages can skip the markdown pipeline entirely
+- [ ] Mount content in VFS
 - [ ] commands
   - [ ] `build` alias of default
   - [ ] `init` set up new project