feat(theme): add top placement for sections

- Add `placement: top|bottom` to the section frontmatter
- Override `DocContent` to render hoisted bands under the page title
- Derive the zebra stripe from list position so split bands stay continuous
- Opt marketing bands out of doc typography with `rp-not-doc`
- Point the legal and privacy contact address at legal@onixbyte.com
- Condense the products pages' body copy into their section frontmatter

theme/index.css

@@ -19,11 +19,16 @@
   padding: 0;
 }
 
-/* Full-bleed marketing sections, driven by `frontmatter.sections`. */
+/* Marketing sections, driven by `frontmatter.sections`. A band is full-bleed
+   when it renders below the article and article-width when `placement: top`
+   puts it inside the doc column. */
 .rp-site-section {
   padding-block: var(--rp-site-section-gap);
 }
 
-.rp-site-section:nth-child(even) {
+/* Zebra striping. Chosen by `HomeSections` from the band's position in the
+   page's whole `sections` list rather than by `:nth-child`, so that bands
+   split across the top and bottom slots keep one continuous stripe. */
+.rp-site-section--tinted {
   background: var(--rp-c-bg-soft);
 }