feat(www): interactive DB viewer hero + max-w-7xl centering (#28)

Replace the static hero screenshot with a self-contained React mockup of the
full Gridline DB viewer (sidebar, table tree, tab bar, fake SQL editor,
data grid, queries/objects/schema-visualizer views, disabled Tools state).

- Add @astrojs/react and mount the island via client:visible
- 16:9 aspect-ratio mockup, hidden on mobile (static image fallback)
- JSON cell popover: solid surface, anchored within the mockup window,
  Escape/outside-click close
- Dependency-free HTML5 drag-to-reorder tabs
- Theme-aware app tokens (canvas, surface-raised, popover bg)
- Site-wide max-w-7xl (was max-w-[1200px]) so sections center on big screens
- Regenerate standalone www/bun.lock for deterministic Dokploy builds

www/astro.config.mjs

@@ -2,6 +2,7 @@
 import { defineConfig } from 'astro/config';
 import tailwindcss from '@tailwindcss/vite';
 import sitemap from '@astrojs/sitemap';
+import react from '@astrojs/react';
 
 // https://astro.build/config
 export default defineConfig({
@@ -12,6 +13,7 @@ export default defineConfig({
     sitemap({
       lastmod: new Date(),
     }),
+    react(),
   ],
   vite: {
     plugins: [tailwindcss()],