fix(openrouter): Gemini 3 tool support, suffix stripping, thought_signature, autocomplete endpoint (#11856)

* fix: multiple OpenRouter provider improvements

- Add google/gemini-3 to tool support prefixes so Gemini 3 models are
  detected as supporting tools via OpenRouter (#8980)
- Strip :free/:extended/:beta suffixes before matching in OpenRouter
  tool support, fixing models like meta-llama/llama-3.2-3b-instruct:free
  not being recognized (#11095)
- Add thought_signature fallback for Gemini models via OpenRouter to
  prevent 400 errors when tool calling (#8980)
- Fix autocomplete/next-edit forcing legacy /completions endpoint on
  OpenRouter, which only supports /chat/completions (#3648)
- Enrich OpenRouter error messages with provider metadata details
  instead of showing generic "Provider returned error" (#11262, #11577)

* fix: remove error enrichment, add TODO for OpenRouter error extraction

* chore: clean up verbose comments and add OpenRouter tool support tests

* style: fix prettier formatting in toolSupport.ts