feat: revamp to dynamic database-first architecture and cleanup phase docs

- Migrate document fetching and CRUD to be PostgreSQL-authoritative
- Remove static section enums and add dynamic listSections query
- Support custom sections and metadata across API, MCP, and Web UI
- Add /api/sections endpoint and update Header, Sidebar, and Forms
- Remove obsolete phase planning docs and modernize README/AGENTS

apps/web/app/api/sections/route.ts

@@ -0,0 +1,15 @@
+import { NextResponse } from "next/server";
+import { listSections } from "@mcpedia/core";
+
+export const dynamic = "force-dynamic";
+
+// GET /api/sections — list all active sections with document counts dynamically from PostgreSQL.
+export async function GET() {
+  try {
+    const sections = await listSections();
+    return NextResponse.json(sections);
+  } catch (err) {
+    const msg = err instanceof Error ? err.message : String(err);
+    return NextResponse.json({ error: msg }, { status: 500 });
+  }
+}