Expose download response-header override options for open and share links

[goanpeca]

Summary

B2 download calls and authorized URLs can override response headers such as content disposition, content type, cache control, and expiration. The extension does not currently expose these options when opening files or creating shareable links.

SDK capability

• Bucket.download(..., { b2ContentDisposition, b2ContentLanguage, b2ContentEncoding, b2ContentType, b2CacheControl, b2Expires })
• Bucket.getDownloadAuthorization(...)
• S3-compatible helpers such as presignGetObjectUrl where applicable

Proposed UI

Extend open/share flows with optional response-header overrides. Keep the default share-link path simple, but allow advanced users to set headers when they need browser download behavior, cache behavior, or explicit content type.

Acceptance criteria

• Share-link creation can optionally set content disposition.
• Share-link creation can optionally set content type and cache-related headers.
• Header override inputs are validated and omitted when blank.
• The generated URL/open operation passes the selected overrides to the SDK.
• Tests cover each supported override field.

Related

• Create shareable download links (presigned URL command with TTL and prefix scope) #62 tracks the base shareable download link command.