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/login/page.tsx

@@ -6,7 +6,7 @@ import Link from "next/link";
 
 // Simple admin login form. POSTs password to /api/auth/login.
 // On success, the API sets an HTTP-only cookie. We don't touch the cookie
-// client-side (it's HttpOnly) — just redirect to the create page after login.
+// client-side (it's HttpOnly) — just redirect to /create after login.
 export default function LoginPage() {
   const router = useRouter();
   const [password, setPassword] = useState("");
@@ -30,7 +30,7 @@ export default function LoginPage() {
         throw new Error(data.error ?? "Login failed");
       }
 
-      router.push("/docs/create");
+      router.push("/create");
     } catch (err) {
       setError(err instanceof Error ? err.message : String(err));
     } finally {
@@ -39,40 +39,46 @@ export default function LoginPage() {
   }
 
   return (
-    <div className="min-h-screen flex items-center justify-center bg-zinc-50 dark:bg-zinc-950">
+    <div className="flex min-h-[60vh] items-center justify-center">
       <div className="w-full max-w-sm">
-        <div className="bg-white dark:bg-zinc-900 p-8 rounded-lg shadow-lg border border-zinc-200 dark:border-zinc-800">
-          <h1 className="text-2xl font-bold mb-6 text-center">MCPedia Admin</h1>
-          {error && (
-            <div className="p-3 bg-red-50 dark:bg-red-900/20 border border-red-200 dark:border-red-800 rounded text-red-800 dark:text-red-200 mb-4">
-              {error}
-            </div>
-          )}
-          <form onSubmit={handleSubmit} className="space-y-4">
-            <div>
-              <label className="block text-sm font-medium mb-1">Password</label>
-              <input
-                type="password"
-                value={password}
-                onChange={(e) => setPassword(e.target.value)}
-                className="w-full px-3 py-2 border border-zinc-300 dark:border-zinc-700 rounded bg-white dark:bg-zinc-900"
-                required
-                autoFocus
-              />
-            </div>
-            <button
-              type="submit"
-              disabled={loading}
-              className="w-full px-4 py-2 bg-zinc-900 dark:bg-zinc-100 text-white dark:text-zinc-900 rounded hover:bg-zinc-800 disabled:opacity-50"
-            >
-              {loading ? "Logging in..." : "Login"}
-            </button>
-          </form>
-        </div>
-        <div className="text-center mt-4">
+        <h1 className="text-2xl font-light text-[#f7f8f8] mb-2">Admin Login</h1>
+        <p className="text-[#8a8f98] text-sm mb-6">
+          Enter your admin password to manage documents.
+        </p>
+
+        {error && (
+          <div className="p-3 mb-4 rounded border border-[#274360] text-[#fca5a5] text-sm">
+            {error}
+          </div>
+        )}
+
+        <form onSubmit={handleSubmit} className="space-y-4">
+          <div>
+            <label className="block text-xs font-medium text-[#d0d6e0] mb-1">
+              Password
+            </label>
+            <input
+              type="password"
+              value={password}
+              onChange={(e) => setPassword(e.target.value)}
+              className="w-full px-3 py-2 bg-[#0f1011] border border-[#23252a] rounded text-[#f7f8f8] focus:outline-none focus:border-[#5e6ad2] focus:ring-1 focus:ring-[#5e6ad2]"
+              required
+              autoFocus
+            />
+          </div>
+          <button
+            type="submit"
+            disabled={loading}
+            className="w-full px-4 py-2 bg-[#5e6ad2] text-white rounded hover:bg-[#7170ff] transition-colors disabled:opacity-50 font-medium text-sm"
+          >
+            {loading ? "Logging in..." : "Login"}
+          </button>
+        </form>
+
+        <div className="mt-6">
           <Link
             href="/"
-            className="text-sm text-zinc-600 dark:text-zinc-400 hover:underline"
+            className="text-sm text-[#8a8f98] hover:text-[#d0d6e0] transition-colors"
           >
             ← Back to home
           </Link>