feat: add Ollama Cloud compatibility

[Shahriar-Hossein]

Summary

• Add a JSON-only compatibility mode for Ollama Cloud models that do not support structured output.
• Automatically retry invalid or incomplete structured responses using JSON-only output.
• Preserve custom authentication headers during both commit generation and diff summarization.
• Tune output limits and reasoning options for GPT-OSS models.
• Validate generated commit subjects and descriptions, including localized descriptions.
• Improve background scanning by preventing overlapping scans and using diff-based fallback summaries.
• Document the Ollama Cloud configuration.

Why

Some Ollama Cloud models, particularly GPT-OSS models, may reject structured-output requests or exhaust their output budget during reasoning. This prevented Commitollama from reliably generating commit messages and descriptions through Ollama Cloud.

Testing

• pnpm lint
• pnpm run typecheck
• pnpm test
• pnpm run package

Results:

• 63 tests passing
• 1 opt-in live Ollama Cloud test skipped during the standard test run
• VSIX packaged successfully

Notes

The live Cloud test can be enabled with:

COMMITOLLAMA_LIVE_MODEL_TEST=1 pnpm test