fix(providers): update the v6 SDK packages and fix Claude and Gemini settings

- Update ai to 6.0.300 and the @ai-sdk providers to their latest v6-line
  versions. @ai-sdk/anthropic 3.0.47 did not know claude-opus-4-7/4-8
  and capped their output at 32000 tokens; 3.0.127 allows 128000
- Drop the fine-grained-tool-streaming beta header for the Anthropic API:
  the provider now streams tool input per tool (eager_input_streaming)
- Claude 4.7 and later reject a non-default temperature/top_p/top_k and
  the extended thinking budget with a 400. A middleware retries once
  without them, so TEMPERATURE and *_THINKING_BUDGET_TOKENS no longer
  break those models
- Prompt caching also reaches Claude on the Anthropic API and OpenRouter;
  before, only Bedrock got a cache marker
- GOOGLE_TOP_K and GOOGLE_TOP_P never reached Gemini: they were sent as
  Google provider options, which drops them. They are call settings now.
  GOOGLE_CANDIDATE_COUNT and GOOGLE_REASONING_EFFORT, which the provider
  does not support, are removed
- Add @ai-sdk/openai-compatible as a direct dependency

env.example

@@ -44,7 +44,6 @@ AI_MODEL=global.anthropic.claude-sonnet-4-5-20250929-v1:0
 # Google Generative AI Configuration
 # GOOGLE_GENERATIVE_AI_API_KEY=...
 # GOOGLE_BASE_URL=https://generativelanguage.googleapis.com/v1beta  # Optional: Custom endpoint
-# GOOGLE_CANDIDATE_COUNT=1                   # Optional: Number of candidates to generate
 # GOOGLE_TOP_K=40                            # Optional: Top K sampling parameter
 # GOOGLE_TOP_P=0.95                          # Optional: Nucleus sampling parameter
 # Note: Gemini 2.5/3 models automatically enable reasoning display (includeThoughts: true)