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.

package.json

@@ -22,6 +22,7 @@
   "scripts": {
     "build": "vite build",
     "compile": "tsc --project ./tsconfig.json --noEmit false",
+    "compile:fast": "tsgo --project ./tsconfig.json --noEmit",
     "eslint": "eslint ./src ./packages/*/src",
     "eslint-fix": "eslint ./src --fix",
     "test": "vitest run",
@@ -46,8 +47,9 @@
     "@vitest/coverage-v8": "^4.0.18",
     "eslint": "^9.8.0",
     "jsdom": "^27.4.0",
+    "@typescript/native-preview": "^7.0.0-dev.20260510.1",
     "tslib": "^2.6.3",
-    "typescript": "~5.8.2",
+    "typescript": "^6.0.3",
     "typescript-eslint": "^8.26.1",
     "vite": "^8.0.10",
     "vitest": "^4.1.5"