Add server, routes, views, CLI, CSS, and integration tests

- Server factory with Fastify plugins (JWT, cookie, multipart, formbody, static)
- Auth middleware: requireAuth preHandler (401 for API, redirect for pages)
- Auth API routes: POST /api/v1/auth/login, POST /api/v1/auth/logout
- File API routes: GET/POST /api/v1/files, DELETE /api/v1/files/:id
- Page routes: /, /login, /logout, /upload, /files, /files/:id/delete, /f/:id, /f/:id/raw
- HTML views: layout, login, upload, file-list, file-view, not-found
- CLI register-user script
- public/style.css dark theme
- Test helpers: createTestApp, loginAs, buildMultipart
- Integration tests for auth API, file API, and page routes (51 tests passing)
- Update CLAUDE.md with red/green TDD and commit instructions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/views/not-found.ts

@@ -0,0 +1,11 @@
+import { layout } from './layout.ts';
+
+export function notFoundPage(): string {
+  return layout('Not found', `
+    <div class="form-container">
+      <h1>404 — Not found</h1>
+      <p>The page or file you requested does not exist.</p>
+      <p><a href="/">Go home</a></p>
+    </div>
+  `);
+}