feat(site): port stitch design system + seed-ready content model

Ports the "Technical Editorial" design sample into real TSX wired to
Payload globals/collections. Home/About/Projects (list+detail)/Contact
pages render against Payload data. Expands schemas (Home principles,
About timeline/skills/gear, Contact channels) to cover the full design
surface. Adds seed script that populates realistic AI-drafted content
for first boot. Defers writing/resume routes per scope cut.

- Design tokens: Material-3 palette + Space Grotesk/Inter typography
  scale + dot-grid + glassmorphism utilities
- Shared layout: Nav, Footer, StatusTerminal, GridOverlay, Button,
  TechChip in src/components/site
- Schemas: expand 5 globals + 6 collections; add auto-slug hook
- Seed: scripts/seed.ts — idempotent upsert for media, categories,
  6 projects, 8 gear, 3 posts, 5 globals; generates placeholder admin
- Contact: form + /api/contact route with optional Turnstile verify
- Rename TURNSTILE_SITE_KEY -> NEXT_PUBLIC_TURNSTILE_SITE_KEY (client)
- Remove dead src/components/SiteHeader|SiteFooter|StatusTerminal

src/app/(frontend)/writing/[slug]/page.tsx

@@ -1,6 +1,4 @@
 import { notFound } from "next/navigation";
-import { SiteHeader } from "@/components/SiteHeader";
-import { SiteFooter } from "@/components/SiteFooter";
 
 type Params = { slug: string };
 
@@ -22,22 +20,16 @@ export default async function PostDetailPage({
   if (!slug) notFound();
 
   return (
-    <>
-      <SiteHeader />
-      <article className="mx-auto max-w-3xl px-6 py-24">
-        <span className="mb-4 block font-label text-xs uppercase tracking-[0.4em] text-secondary">
-          POST //{" "}
-          <code className="text-on-surface-variant">{slug}</code>
-        </span>
-        <h1 className="mb-6 font-headline text-4xl font-bold tracking-tight md:text-6xl">
-          Post detail
-        </h1>
-        <p className="font-body text-lg text-on-surface-variant">
-          Body renders from Payload{" "}
-          <code className="font-label text-primary">posts</code> once wired.
-        </p>
-      </article>
-      <SiteFooter />
-    </>
+    <article className="mx-auto max-w-3xl px-6 py-24">
+      <span className="mb-4 block font-label text-xs uppercase tracking-[0.4em] text-secondary">
+        POST //{" "}
+        <code className="text-on-surface-variant">{slug}</code>
+      </span>
+      <h1 className="display-sm mb-6 text-on-surface">Post detail</h1>
+      <p className="body-md">
+        Body renders from Payload{" "}
+        <code className="font-label text-primary">posts</code> once wired.
+      </p>
+    </article>
   );
 }