feat(jtk): port attachments command

[rianjs]

Port attachment management commands from jira-ticket-cli PR #60.

Files to create:

• tools/jtk/api/attachments.go - API client
• tools/jtk/internal/cmd/attachments/attachments.go - Commands

Commands:

• jtk attachments list <issue-key>
• jtk attachments add <issue-key> --file <path> (multiple --file supported)
• jtk attachments get <attachment-id> --output <dir>
• jtk attachments delete <attachment-id>

API functions:

• GetIssueAttachments, GetAttachment, AddAttachment, DeleteAttachment, DownloadAttachment
• FormatFileSize, FlexibleID helpers

Source: open-cli-collective/jira-ticket-cli#60

[rianjs]

Implementation Plan

Changes:

1. Create tools/jtk/api/attachments.go

   • Attachment struct with FlexibleID for ID handling
   • GetIssueAttachments(issueKey) - list attachments for an issue
   • GetAttachment(id) - get attachment metadata
   • AddAttachment(issueKey, filePath) - upload file
   • DeleteAttachment(id) - delete attachment
   • DownloadAttachment(attachment, outputPath) - download file
   • FormatFileSize(bytes) helper

2. Create tools/jtk/api/attachments_test.go

   • Unit tests for all API functions
   • Tests for FlexibleID unmarshaling

3. Create tools/jtk/internal/cmd/attachments/attachments.go

   • jtk attachments list <issue-key>
   • jtk attachments add <issue-key> --file <path> (multiple files)
   • jtk attachments get <id> --output <dir>
   • jtk attachments delete <id>

4. Update tools/jtk/cmd/jtk/main.go

   • Register attachments command

Source: jira-ticket-cli PR #60