chore(ts): bump TypeScript 5.8 → 6.0 and add tsgo for fast type-checking

- typescript: ~5.8.2 → ^6.0.3 (matches Nitro-V3 client)
- adds @typescript/native-preview (tsgo) as TypeScript 7 preview
- new `compile:fast` script using tsgo (~7× faster: 2.5s vs 17.6s)
- tsconfig cleanup ahead of TypeScript 7 deprecations:
  - removed `baseUrl` (unused: no `paths` mappings on this project)
  - removed `downlevelIteration` (target ES2022 makes it a no-op)
  - `moduleResolution`: "Node" → "bundler" (vite consumes the renderer)

Compile errors: 28 → 29. Net +1 because TS 6's tightened lib types flag
two pre-existing crypto calls (WsSessionCrypto.ts:43,48) and resolves one
prior false positive. All errors are in pre-existing code, unrelated to
the new event/snapshot APIs from 791b8ad.

tsconfig.json

@@ -1,17 +1,15 @@
 {
   "compileOnSave": false,
   "compilerOptions": {
-    "baseUrl": "./src",
     "outDir": "./dist",
     "sourceMap": false,
     "declaration": true,
     "experimentalDecorators": true,
-    "moduleResolution": "Node",
+    "moduleResolution": "bundler",
     "esModuleInterop": true,
     "importHelpers": true,
     "isolatedModules": true,
     "resolveJsonModule": true,
-    "downlevelIteration": true,
     "allowSyntheticDefaultImports": true,
     "allowJs": true,
     "skipLibCheck": true,