Add Palm2-compatible Google AI provider

[l8888888]

Closes #279
/claim #279

Summary

• Reworks the Google Generative Language provider into a direct REST-based Palm2AI class with a GeminiAI compatibility export
• Adds typed contents, generation config, responses, JSON response mode, retry support, and text helper output
• Adds mocked unit tests under src/ai/src/tests/palm2/
• Adds a jsonnet-driven chat example where prompts live in jsonnet instead of TypeScript

Validation

• npm test -- --run src/ai/src/tests/palm2/gemini.test.ts
• npm run build

Note: the example is included as source documentation for local usage after this package build includes the new Palm2AI export.