feat(web): full layout overhaul — Linear design system

Complete UI/UX overhaul, not just style changes:

Layout:
- Dark-mode-first (near-black #08090a canvas, whiteOpacity borders)
- Sticky header with brand + nav + theme toggle
- Sticky sidebar (xl+) with hierarchical doc tree
- Main content in max-w-3xl centered column
- Inter font system (via @font-face + CSS vars)
- Font feature settings cv01/ss03 for Linear-geometric Inter

Components rewritten in Linear aesthetic:
- Homepage: editorial-style doc listing with tags, section headers
- Doc page: breadcrumb-style nav links, metadata bar (author/date/tags),
  clean prose, Related + History sections
- TOC: rehype-slug heading anchors + github-slugger matching
- Create/Edit: inline form with Linear-style inputs/buttons
- Login: centered card-style, brand-indigo CTA button
- Docs index: sectioned listing with tag previews
- Search: dark-themed search with result cards + snippets
- ThemeToggle: system-default + localStorage persistence

Typography:
- prose with custom Tailwind classes matching Linear's:
  headings #f7f8f8 font-light, body #d0d6e0,
  links #7170ff with hover #828fff,
  code blocks #191a1b bg with #23252a border

New deps: rehype-slug (heading anchors), github-slugger (TOC matching)
Files: layout.tsx (overhaul), page.tsx, create/, login/, docs/,
       [section]/[...slug]/page.tsx, Sidebar.tsx, ThemeToggle.tsx,
       TOC.tsx, DocForm.tsx, Markdown.tsx, Search page

apps/web/app/create/page.tsx

@@ -3,24 +3,23 @@ import { cookies } from "next/headers";
 import DocForm from "@/components/DocForm";
 import Link from "next/link";
 
-// GET /create — show the document creation form.
-// Auth: requires the mcpedia_admin cookie (set via /api/auth/login).
-export const dynamic = "force-dynamic";
-
-export default async function CreateDocPage() {
+// GET /create — show the document create form.
+// Requires admin cookie auth.
+export default async function CreatePage() {
   const cookieStore = await cookies();
   const canEdit = cookieStore.get("mcpedia_admin")?.value != null;
-
   if (!canEdit) {
     return (
-      <div className="p-8 max-w-md mx-auto">
-        <h1 className="text-xl font-semibold mb-4">Authentication required</h1>
-        <p className="text-zinc-600 dark:text-zinc-400 mb-4">
+      <div className="text-center py-16">
+        <h1 className="text-2xl font-light text-[#f7f8f8] mb-4">
+          Authentication required
+        </h1>
+        <p className="text-[#8a8f98] mb-6">
           You must be logged in to create documents.
         </p>
         <Link
           href="/login"
-          className="px-4 py-2 bg-zinc-900 dark:bg-zinc-100 text-white dark:text-zinc-900 rounded"
+          className="inline-flex items-center gap-2 px-4 py-2 rounded bg-[#5e6ad2] text-white hover:bg-[#7170ff] transition-colors font-medium text-sm"
         >
           Login
         </Link>
@@ -29,9 +28,17 @@ export default async function CreateDocPage() {
   }
 
   return (
-    <div className="p-8">
-      <h1 className="text-2xl font-bold mb-6">Create Document</h1>
-      <DocForm mode="create" slug="" secret={WEBHOOK_SECRET} />
+    <div>
+      <Link
+        href="/"
+        className="text-xs text-[#8a8f98] hover:text-[#d0d6e0] mb-4 inline-block"
+      >
+        ← Back
+      </Link>
+      <h1 className="text-2xl font-light text-[#f7f8f8] mb-6">
+        Create Document
+      </h1>
+      <DocForm mode="create" secret={WEBHOOK_SECRET} />
     </div>
   );
 }