revert: restore tsconfig.base.json needed by packages/adapter-*

37a57d5 removed this file as an orphan, but 4 workspace packages
(adapter-utils/claude/codex/gemini) still extend it via
"extends": "../../tsconfig.base.json". Vite's esbuild transform
follows the chain at build time, so the file is load-bearing for
electron-vite build despite having no direct root tsconfig reference.

tsconfig.base.json

@@ -0,0 +1,18 @@
+{
+  "compilerOptions": {
+    "target": "ES2023",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "esModuleInterop": true,
+    "strict": true,
+    "skipLibCheck": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "outDir": "dist",
+    "rootDir": "src",
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "isolatedModules": true
+  }
+}