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/dashboard.mobile-layout.test.tsx

@@ -1,14 +0,0 @@
-import { describe, expect, it } from 'vitest';
-import { readFileSync } from 'node:fs';
-import { resolve } from 'node:path';
-
-describe('Dashboard mobile layout', () => {
-  it('uses the shared mobile breakpoint to collapse fixed desktop grids', () => {
-    const source = readFileSync(resolve(process.cwd(), 'src/web/pages/Dashboard.tsx'), 'utf8');
-
-    expect(source).toContain('import { useIsMobile } from "../components/useIsMobile.js";');
-    expect(source).toContain('const isMobile = useIsMobile()');
-    expect(source).toContain('gridTemplateColumns: isMobile ? "1fr" : "1fr 1fr"');
-    expect(source).toContain('gridTemplateColumns: isMobile ? "1fr" : "1fr 300px"');
-  });
-});