refactor: centralize section config — remove all hardcoded section lists

- New packages/config/src/sections.ts: SECTIONS, SECTIONS_BY_ID, SECTION_IDS
  (no Node.js built-in imports — safe for client components)
- New package entrypoint: @mcpedia/config/sections (exports only sections.ts)
- Client components import from @mcpedia/config/sections (no node:fs in bundle)
- Server components import from @mcpedia/config (has env/fs, server-only)
- Removed hardcoded SECTIONS/SECTION_LABEL/SECTION_ICON from:
  - [section]/page.tsx (was inline array)
  - [section]/[...slug]/page.tsx (was hardcoded Record maps)
  - Sidebar.tsx (was inline array)
  - layout.tsx (was inline array)
  - page.tsx (was inline array)
  - create/page.tsx (was inline array via SECTIONS import)
- Added @mcpedia/config/sections entrypoint to package.json exports

apps/web/app/[section]/page.tsx

@@ -1,5 +1,6 @@
 import Link from "next/link";
 import { listDocuments } from "@mcpedia/core";
+import { SECTIONS } from "@mcpedia/config/sections";
 
 export const dynamic = "force-dynamic";
 
@@ -12,18 +13,6 @@ interface DocMeta {
   path: string;
 }
 
-const SECTIONS: { id: string; label: string; icon: string; desc: string }[] = [
-  {
-    id: "docs",
-    label: "Documentation",
-    icon: "📄",
-    desc: "Setup guides, API references, and protocol specs.",
-  },
-  { id: "writeups", label: "Writeups", icon: "📝", desc: "Post-mortems, debugging stories, and case studies." },
-  { id: "research", label: "Research", icon: "🔬", desc: "Deep-dive analysis, architecture notes, and experiments." },
-  { id: "notes", label: "Notes", icon: "📌", desc: "Quick references, patterns, and gotchas." },
-];
-
 /**
  * Build a hierarchical folder tree from a flat list of documents.
  * Each node is either a folder (has children) or a leaf doc.
@@ -68,8 +57,6 @@ function buildFolderTree(docs: DocMeta[], section: string): TreeNode[] {
       if (isLeaf) {
         node.doc = doc;
         node.docCount = 1;
-      } else {
-        // This is a folder — count will be accumulated below
       }
       current = node.children;
     }