feat(web): add interactive Architecture Explorer to homepage

D3 force-directed graph with 8 nodes (6 core abstractions + User/REPL),
14 directed edges, hover tooltips, click-to-navigate, drag to rearrange,
dark mode support. Replaces static diagram with an interactive showpiece.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: alejandrobalderas

web/bun.lock

@@ -12,7 +12,9 @@
     "@astrojs/react": "^4.2.0",
     "@fontsource-variable/jetbrains-mono": "^5.1.3",
     "@fontsource-variable/source-serif-4": "^5.1.1",
+    "@types/d3": "^7.4.3",
     "astro": "^5.7.0",
+    "d3": "^7.9.0",
     "mermaid": "^11.4.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0"