chore: add changesets for openai-base extraction

Author: AlemTuzlak

.changeset/add-ai-utils-package.md

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+---
+'@tanstack/ai-utils': minor
+---
+
+New package: shared provider-agnostic utilities for TanStack AI adapters. Includes `generateId`, `getApiKeyFromEnv`, `transformNullsToUndefined`, and `ModelMeta` types with `defineModelMeta` validation helper. Zero runtime dependencies.

.changeset/add-openai-base-package.md

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+---
+'@tanstack/openai-base': minor
+---
+
+New package: shared base adapters and utilities for OpenAI-compatible providers. Includes Chat Completions and Responses API text adapter base classes, image/summarize/transcription/TTS/video adapter base classes, schema converter, 15 tool converters, and shared types. Providers extend these base classes to reduce duplication and ensure consistent behavior.

.changeset/refactor-providers-to-shared-packages.md

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+---
+'@tanstack/ai-openai': patch
+'@tanstack/ai-grok': patch
+'@tanstack/ai-groq': patch
+'@tanstack/ai-openrouter': patch
+'@tanstack/ai-ollama': patch
+'@tanstack/ai-anthropic': patch
+'@tanstack/ai-gemini': patch
+'@tanstack/ai-fal': patch
+'@tanstack/ai-elevenlabs': patch
+---
+
+Internal refactor: delegate shared utilities to `@tanstack/ai-utils` and OpenAI-compatible adapter logic to `@tanstack/openai-base`. No breaking changes — all public APIs remain identical.