feat(theme): add site footer and marketing sections

- Add SiteFooter, rendered through the Layout bottom slot so it appears on
  every page type. themeConfig.footer is deliberately left unset: setting
  it would render the built-in HomeFooter as well, on the home page only.
- Add a frontmatter-driven section system (advantages, contentGrid,
  techStack, cases and cta) with a single ordered array, so bands can be
  reordered or removed without touching code.
- Bands render only when they have content, so an unfilled page degrades
  to its heading rather than showing empty boxes.
- Add a SHOW_COPY_PLACEHOLDERS flag for drafting, false by default.

theme/components/sections/Cases.tsx

@@ -0,0 +1,102 @@
+import { useCallback, useEffect, useState } from "react"
+import { arr, str, type CaseStudy } from "./types"
+
+const ROTATE_MS = 8000
+
+/**
+ * Customer case-study carousel.
+ *
+ * TODO(copy): populate `frontmatter.sections` with real case studies. With no
+ * items this renders nothing; with exactly one it degrades to a static card.
+ *
+ * Rotation is suspended when the visitor prefers reduced motion, and pauses
+ * while the carousel is hovered or focused.
+ */
+export function Cases({ items }: { items?: CaseStudy[] }) {
+  const studies = (arr<CaseStudy>(items) ?? []).filter((item) => str(item?.company))
+  const [active, setActive] = useState(0)
+  const [paused, setPaused] = useState(false)
+
+  const count = studies.length
+  const go = useCallback(
+    (next: number) => setActive(count > 0 ? ((next % count) + count) % count : 0),
+    [count]
+  )
+
+  useEffect(() => {
+    if (count <= 1 || paused) return
+    if (
+      typeof window !== "undefined" &&
+      window.matchMedia?.("(prefers-reduced-motion: reduce)").matches
+    ) {
+      return
+    }
+    const timer = window.setInterval(() => setActive((current) => (current + 1) % count), ROTATE_MS)
+    return () => window.clearInterval(timer)
+  }, [count, paused])
+
+  if (count === 0) return null
+
+  const current = studies[Math.min(active, count - 1)]
+  const company = str(current.company) ?? ""
+  const quote = str(current.quote)
+  const details = str(current.details)
+  const author = str(current.author)
+  const role = str(current.role)
+  const link = str(current.link)
+  const logo = str(current.logo)
+
+  return (
+    <div
+      className="rounded-xl border border-(--rp-c-divider-light) bg-(--rp-c-bg-soft) p-8"
+      onMouseEnter={() => setPaused(true)}
+      onMouseLeave={() => setPaused(false)}
+      onFocus={() => setPaused(true)}
+      onBlur={() => setPaused(false)}>
+      <figure className="m-0 flex flex-col items-center gap-6 text-center">
+        {logo && <img src={logo} alt={company} height={40} className="h-10 w-auto" />}
+        {quote && (
+          <blockquote className="m-0 max-w-3xl text-lg leading-relaxed text-(--rp-c-text-1)">
+            {quote}
+          </blockquote>
+        )}
+        {/* Without an approved testimonial, describe the engagement instead. */}
+        {!quote && details && (
+          <p className="m-0 max-w-2xl text-base leading-relaxed text-(--rp-c-text-1)">{details}</p>
+        )}
+        <figcaption className="text-sm text-(--rp-c-text-2)">
+          {author && <span className="font-medium text-(--rp-c-text-1)">{author}</span>}
+          {author && role && <span> · </span>}
+          {role}
+          {link ? (
+            <>
+              {" · "}
+              <a className="rp-link" href={link}>
+                {company}
+              </a>
+            </>
+          ) : (
+            company && <span> · {company}</span>
+          )}
+        </figcaption>
+      </figure>
+
+      {count > 1 && (
+        <div className="mt-6 flex justify-center gap-2">
+          {studies.map((study, index) => (
+            <button
+              key={`${str(study.company)}-${index}`}
+              type="button"
+              aria-label={str(study.company)}
+              aria-current={index === active}
+              onClick={() => go(index)}
+              className={`h-2 w-2 cursor-pointer rounded-full border-0 p-0 transition-colors ${
+                index === active ? "bg-(--rp-c-brand)" : "bg-(--rp-c-divider)"
+              }`}
+            />
+          ))}
+        </div>
+      )}
+    </div>
+  )
+}