Revert "feat: OpenAI provider/types/UI updates; provider state persistence"

[daniel-lxs]

This PR reverts PR #6864 to prepare for splitting the changes into smaller, more manageable pull requests.

The original PR introduced multiple features and changes that would be better reviewed and merged separately.

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Important

Reverts PR #6864, removing OpenAI provider and GPT-5 model features, including schema changes, test removals, and UI updates.

• Behavior:
  • Reverts changes from PR GPT5 OpenAI Fix #6864, removing features related to OpenAI provider and GPT-5 models.
  • Removes GPT-5 specific handling in openai-native.ts and index.ts.
• Schemas:
  • Removes metadata field from clineMessageSchema in message.ts.
  • Removes supportsVerbosity from modelInfoSchema in model.ts.
• Tests:
  • Removes tests for GPT-5 models in openai-native.spec.ts.
• UI:
  • Removes reasoning effort "minimal" option from provider-settings.ts and related UI components.
  • Updates i18n files to remove "minimal" reasoning effort option.

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[roomote]

Thank you for this clean revert! I've reviewed the changes and confirmed that all GPT-5 related features have been properly removed across the codebase.

The revert successfully removes:

• GPT-5 model definitions (gpt-5, gpt-5-mini, gpt-5-nano)
• The "minimal" reasoning effort option
• Verbosity control features
• GPT-5 metadata persistence
• Responses API implementation
• Related test coverage
• UI components and i18n entries

One minor suggestion: Could you provide more context in the PR description about which specific aspects will be split into separate PRs? This would help reviewers understand the planned breakdown.