feat: add node: protocol to all Node.js built-in imports for bundler compatibility

- Updated all fs, path, crypto, os, url, util, events, http, https, net, child_process, stream, and zlib imports
- Changed both static imports and dynamic imports to use node: protocol
- This makes Brainy more bundler-friendly by explicitly marking Node.js built-ins
- Prevents bundlers from attempting to polyfill or bundle these modules
- Reduces bundle size for web applications using Brainy
- Improves tree-shaking and dead code elimination

Benefits for external bundlers:
- Clear distinction between Node.js built-ins and external dependencies
- No ambiguity about what needs polyfilling
- Smaller bundles for browser builds
- Better compatibility with modern bundlers (Webpack 5, Vite, Rollup, esbuild)

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

src/critical/model-guardian.ts

@@ -11,10 +11,10 @@
  * 4. System MUST fail fast if model unavailable in production
  */
 
-import { existsSync } from 'fs'
-import { readFile, mkdir, writeFile, stat } from 'fs/promises'
-import { join, dirname } from 'path'
-import { createHash } from 'crypto'
+import { existsSync } from 'node:fs'
+import { readFile, mkdir, writeFile, stat } from 'node:fs/promises'
+import { join, dirname } from 'node:path'
+import { createHash } from 'node:crypto'
 import { env } from '@huggingface/transformers'
 
 // CRITICAL: These values MUST NEVER CHANGE
@@ -207,8 +207,8 @@ export class ModelGuardian {
    */
   private async computeFileHash(filePath: string): Promise<string> {
     try {
-      const { readFile } = await import('fs/promises')
-      const { createHash } = await import('crypto')
+      const { readFile } = await import('node:fs/promises')
+      const { createHash } = await import('node:crypto')
       const fileBuffer = await readFile(filePath)
       const hash = createHash('sha256').update(fileBuffer).digest('hex')
       return hash