build: typecheck with tsc -b to match the production build

The `typecheck` script ran `tsc --noEmit` against the root tsconfig, which has
`files: []` and only project references — so without `-b` it checked nothing in
src and let real type errors (e.g. theme_id) reach Docker CI. Switch to `tsc -b`
(same as the build) so pre-commit and the Quality job catch them locally.

ha-relevant: no

frontend/package.json

@@ -7,7 +7,7 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "eslint .",
-    "typecheck": "tsc --noEmit",
+    "typecheck": "tsc -b",
     "test": "vitest run",
     "test:watch": "vitest",
     "test:coverage": "vitest run --coverage",