refactor: purge Node.js, Rust is the one true backend

- Moved boosapi-rs/* to repo root
- Deleted all Node.js source (src/server/, src/web/, scripts/)
- Deleted node_modules, package.json, tsconfig, vite.config
- Updated .gitignore and AGENTS.md for Rust-only stack
- Fixed static file path for frontend dist/web/
- Dockerfile stays the same (already Rust-only)
- Kept dist/web/ for Rust static serving

src/web/pages/sites.mobile.test.tsx

@@ -1,10 +0,0 @@
-import { describe, expect, it } from 'vitest';
-import { readFileSync } from 'node:fs';
-import { resolve } from 'node:path';
-
-describe('Sites mobile layout', () => {
-  it('includes mobile-card usage in Sites page', () => {
-    const source = readFileSync(resolve(process.cwd(), 'src/web/pages/Sites.tsx'), 'utf8');
-    expect(source).toContain('mobile-card');
-  });
-});