feat: add article page and not found component with markdown rendering

CLAUDE.md

@@ -34,6 +34,7 @@ docker compose -f docker/docker-compose.yml up -d
 This is a **Next.js 16 App Router** full-stack blog with TypeScript. The structure separates concerns into three main layers:
 
 ### Frontend (`src/app/` + `src/ui/`)
+
 - **Pages** live in `src/app/(pages)/` using route groups
 - **API routes** live in `src/app/api/` (Next.js Route Handlers)
 - **Components** in `src/ui/components/internal/` (custom) and `src/ui/components/shadcn/` (shadcn/ui generated)
@@ -41,7 +42,9 @@ This is a **Next.js 16 App Router** full-stack blog with TypeScript. The structu
 - Root layout at `src/app/layout.tsx` mounts all providers; `/` redirects to `/home` via `next.config.ts`
 
 ### Backend (`src/lib/`)
+
 Domain-driven feature modules — each feature lives in `src/lib/feature/<feature>/` with:
+
 - `*.entity.ts` — TypeORM entity definition
 - `*.model.ts` — DTOs and interfaces (Zod schemas live here too)
 - `*.service.ts` — Business logic (CRUD, validation, no HTTP concerns)
@@ -50,20 +53,24 @@ Domain-driven feature modules — each feature lives in `src/lib/feature/<featur
 Current features: `user/`, `article/`
 
 ### Key Integrations
+
 - **Auth:** Clerk (`@clerk/nextjs`) handles auth. On sign-in, `/api/user/sync` syncs the Clerk user into PostgreSQL via `user.service.ts`. Sessions are stored server-side via `iron-session` (`src/lib/session/`).
 - **Database:** PostgreSQL 16 via TypeORM. `src/lib/db/data-source.ts` is used at runtime; `src/lib/db/data-source.cli.ts` is used by the TypeORM CLI. Entities are exported from `src/lib/db/entities.ts`.
 - **Storage:** `src/lib/storage/` provides a `StorageProvider` interface with an `S3StorageAdapter` implementation (AWS SDK v3). The factory in `storage.factory.ts` selects the provider; `storage.ts` exports the singleton. `put()` returns a presigned URL.
 - **Migrations:** SQL migrations in `migrations/` directory. Run via TypeORM CLI, not auto-run.
 
 ### State management
+
 - **Server state:** React Query (`@tanstack/react-query`) for async data fetching
 - **Client state:** Jotai atoms for local UI state
 - **Forms:** React Hook Form + Zod validation
 
 ### Testing
+
 - Jest with `ts-jest`; tests in `tests/` mirroring `src/lib/` structure
 - PostgreSQL integration tests use `@testcontainers/postgresql` (requires Docker)
 - S3 tests use `aws-sdk-client-mock`
 
 ### Local environment
+
 Docker Compose starts PostgreSQL on port **5332** and Rustfs (S3-compatible) on ports **9000/9001**. Environment variables are in `.env`; key ones: `DATABASE_URL`, `SESSION_SECRET`, `CLERK_*`, `S3_*`.