[Gemini] Hardcoded thinking_level="minimal" breaks gemini-flash-latest and Pro models

## Observed symptom [Bug] Hardcoded thinking_level="minimal" breaks the default `gemini-flash-latest` and all Pro models (400 INVALID_ARGUMENT) Summary `GeminiProvider` unconditionally sets `thinking_level="minimal"` for every non-Gemma model. As of today the API rejects MINIMAL on Gemini 3.7 and 3.8, and on every Pro model I tested, with HTTP 400. The bare `except Exception` in `get_response` then flattens that into the generic "An error occurred while processing the response." This currently breaks the **default** configuration: the shipped default is `gemini-flash-latest`, which Google now resolves to `gemini-3.8-flash`. Root cause `Windows_and_Linux/aiprovider.py`, in `_build_config`: `if not is_gemma: ` Exact API response: `400 INVALID_ARGUMENT ` Gemma is unaffected only because `is_gemma` skips the block entirely — which is why "switch to Gemma" appears to fix it. Evidence Same request shape, one key, only `model` varying (`maxOutputTokens: 1000`, `temperature: 1.0`, `thinkingConfig.thinkingLevel: "minimal"`): Dropping `th ## Literal error text ``` 400 INVALID_ARGUMENT Thinking level MINIMAL is not supported for this model. Please retry with other thinking level. ``` ## Environment GitHub issue theJayTea/WritingTools #282; state=open ## Trigger / context Public GitHub report in theJayTea/WritingTools (FRESH_30D). ## Source evidence - https://github.com/theJayTea/WritingTools/issues/282 (2026-09-11T06:47:02Z) — evidence_class: PRIMARY_ISSUE_REPORT — GitHub issue #282 (open) ## Freshness - classification: FRESH_30D - retrieved_at: 2026-10-02T09:40:08.726088Z - scout_id: C72e2b5baa5 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.