feat: Fix product tables and responsive fonts

- Add product detail page ([slug].astro) with table rendering
- Display productTables from site-config.ts on product pages
- Add responsive font scaling for large screens (1280px+)
- Base font scales from 16px to 24px on 4K displays
- All text elements use responsive sizing (md/lg/xl breakpoints)
- Tables styled with green headers and alternating rows
- Add comprehensive documentation (FIXES_SUMMARY.md)

Fixes:
- Product specification tables now visible on product pages
- Font too small on large screens - now responsive

AGENTS.md

@@ -0,0 +1,95 @@
+# DEAL PLUS TECH - PROJECT KNOWLEDGE BASE
+
+**Generated:** 2026-03-01
+**Commit:** 13436b4
+**Branch:** main
+
+## OVERVIEW
+
+Thai corporate website for pipe/HVAC materials supplier. Next.js 14 App Router + TypeScript + Tailwind CSS. Thai language content with Thai URL support.
+
+## STRUCTURE
+
+```
+src/
+├── app/           # Next.js App Router pages
+├── components/    # UI, layout, analytics components
+├── content/       # Blog markdown files
+├── data/          # Product catalog & site config (HUGE)
+├── lib/           # Utility functions
+├── styles/        # Global CSS + Tailwind
+└── types/         # TypeScript interfaces
+```
+
+## WHERE TO LOOK
+
+| Task | Location | Notes |
+|------|----------|-------|
+| Add/edit pages | `src/app/*/page.tsx` | App Router conventions |
+| Add products | `src/data/site-config.ts` | ProductCategory array |
+| Add product tables | `src/data/product-tables.ts` | Table data for specs |
+| UI components | `src/components/ui/` | Button, Card, Badge |
+| Layout | `src/components/layout/` | Header, Footer, FloatingContact |
+| Types | `src/types/index.ts` | All interfaces |
+| Styling | `src/styles/globals.css` | Custom component classes |
+| SEO/Metadata | `src/app/layout.tsx` | Root metadata + schema |
+
+## CONVENTIONS
+
+**Thai-first content**: All UI text, URLs, metadata in Thai. English `nameEn` fields for product IDs.
+
+**URL format**: Thai URLs with trailing slash (e.g., `/ท่อพีพีอาร์ตราช้าง/`)
+
+**Product data structure**: Each product in `productCategories` has:
+- Thai `name`, `description`, `seoContent`
+- English `nameEn`, `id`, `slug`
+- `specifications[]`, `features[]`, `applications[]`, `faq[]`
+- `schemaData` for structured data
+- Optional `productTables[]` for spec tables
+
+**Styling**: Tailwind + custom classes in globals.css:
+- `.btn-primary`, `.btn-secondary`, `.btn-outline`
+- `.card`, `.card-industrial`
+- `.section-title`, `.section-subtitle`
+
+**Font**: Kanit (Thai Google Font) via `next/font/google`
+
+**Path alias**: `@/*` maps to `./src/*`
+
+## ANTI-PATTERNS (THIS PROJECT)
+
+- **DO NOT** use `output: 'standalone'` in dev mode (breaks HMR)
+- **DO NOT** hardcode contact info - use `siteConfig` from `@/data/site-config`
+- **DO NOT** add tests - project has no test infrastructure
+- **DO NOT** use `as any` or `@ts-ignore` - strict mode enabled
+
+## UNIQUE STYLES
+
+**Design System**: Industrial/construction theme with:
+- Primary green (#22c55e) - trust, growth
+- Secondary slate grays - professional, industrial
+- Accent yellow - highlights
+- Industrial-specific shadows and gradients
+
+**Product pages**: SEO-heavy with structured data (LocalBusiness schema, Product schema)
+
+**Blog**: Headless WordPress integration via `NEXT_PUBLIC_WORDPRESS_API_URL`
+
+**Image optimization**: AVIF/WebP auto-converted, Thai domain patterns in `next.config.mjs`
+
+## COMMANDS
+
+```bash
+npm run dev      # Development server (localhost:3000)
+npm run build    # Production build
+npm run start    # Production server
+npm run lint     # ESLint check
+```
+
+## NOTES
+
+- No CI/CD configured - manual deployments
+- Environment variables in `.env.local` (copy from `.env.example`)
+- Large data files in `src/data/` - edit with care
+- Thai URLs require URL-encoded characters in some contexts
+- `public/llm.txt` contains AI-readable content for the site