feat(bom): add Get Prompt modal for LLM and fix product name resolution (#11)

### Summary of Changes
- Added 'Get Prompt' button and ProductBomPromptModal dialog on /products/:id/bom.
- Formats product ID, variants, and raw material inventory into a structured prompt for LLMs.
- Fixed backend bug in GET /products/:id?lang=all that wiped product.name when no translations existed.
- Added multi-level fallback in frontend to ensure product name never shows 'Unknown Product'.

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Co-authored-by: Your Name <you@example.com>
Reviewed-on: #11
Co-authored-by: antigravity-bot <bot@kittisak.com>

apps/backend/src/routes/products.ts

@@ -471,9 +471,9 @@ export const productsRoute = new Elysia({ prefix: "/products" })
     if (!product || (!includeDeleted && product.isDeleted)) return status(404, { message: "Product not found" });
 
     if (lang === 'all') {
-      const nameObj: any = {};
-      const descObj: any = {};
-      const detailsObj: any = {};
+      const nameObj: any = product.name ? { th: product.name } : {};
+      const descObj: any = product.description ? { th: product.description } : {};
+      const detailsObj: any = product.details ? { th: product.details } : {};
       product.translations.forEach((t: any) => {
          nameObj[t.langCode] = t.name;
          descObj[t.langCode] = t.description;