feat(ai): Create unified AI package with OpenAI, Anthropic, and Gemini support

- Set up @mariozechner/ai package structure following monorepo patterns
- Install OpenAI, Anthropic, and Google Gemini SDK dependencies
- Document comprehensive API investigation for all three providers
- Design minimal unified API with streaming-first architecture
- Add models.dev integration for pricing and capabilities
- Implement automatic caching strategy for all providers
- Update project documentation with package creation guide

packages/ai/tsconfig.build.json

@@ -0,0 +1,9 @@
+{
+	"extends": "../../tsconfig.base.json",
+	"compilerOptions": {
+		"outDir": "./dist",
+		"rootDir": "./src"
+	},
+	"include": ["src/**/*"],
+	"exclude": ["node_modules", "dist"]
+}