fix: preserve object MIME types and download names

[cxymds]

Description

Uploading files through the Console could persist a browser's generic MIME type even when the object name provided a more specific type. This caused archive objects such as test.tar.xz to be stored as application/x-compressed, and direct browser downloads could be saved with the wrong extension. The upload resolver now uses shared filename MIME inference when the browser type is generic, including compound archive suffixes, while preserving specific browser types. Download-only presigned URLs now request an explicit RFC 5987 attachment filename without changing preview or share URLs.

Type of Change

• Bug fix (non-breaking change)
• New feature (non-breaking change)
• Breaking change (breaking change)
• Documentation update
• Code refactoring
• Test improvements
• Security fix

Testing

• Unit tests added/updated
• Manual testing completed

pnpm type-check
pnpm lint
pnpm format:check
pnpm test:run

All checks passed; the test suite reported 599 passing tests.

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

Closes rustfs/rustfs#8027

Screenshots (if applicable)

N/A: this change affects upload metadata and download response headers; no new visual UI is introduced.

Additional Notes

The server continues to preserve explicitly supplied S3 metadata. Only download actions request response-content-disposition; preview and shared temporary URLs retain their existing inline behavior.