feat: add download, cat, and ls commands

[pcfreak30]

Three new commands for accessing pinned IPFS content:

• pinner download [/] — save content to disk
• pinner cat [/] — stream content to stdout
• pinner ls [/] — list directory contents

Supports CID paths for accessing nested content (e.g. CID/subdir/file).
Listing a file shows metadata instead of erroring. JSON output uses
structs with proper tags — single object per command, lowercase keys.

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This PR adds three new CLI commands for interacting with pinned IPFS content: download, cat, and ls.

New Commands:

• download – Downloads pinned content from IPFS to a local file. Supports CID paths (e.g., CID/path/to/file) to download specific files from a directory. Includes --output/-o to specify the output path, --force to overwrite existing files, and --dry-run to preview the operation. Displays CID, local path, file size, gateway URL, and download duration.

• cat – Streams IPFS content directly to stdout. Supports CID paths for streaming specific files from a directory. Useful for piping content to other commands (e.g., pinner cat QmHash | jq .).

• ls – Lists the contents of an IPFS directory, showing file names, types (file/directory), and sizes. Supports --limit to cap the number of entries. If the path targets a file rather than a directory, it gracefully shows the file's metadata instead of erroring.

Supporting changes:

• Added DownloadService interface and default implementation with methods for downloading, streaming, listing directories, and checking file sizes, backed by the ipfs-sdk package
• Added IPFS path parsing (CID + optional subpath) and authentication handling including automatic JWT exchange for API keys
• Added ErrDownloadFailed error type and registered DownloadService in the mockery configuration
• Updated root command to register the new commands and updated their help text
• Added comprehensive unit tests for all three command handlers and the service factory

[github-actions]

Code Coverage Report

Total Coverage: 34.6%

Generated from commit: 3d97fcf
Repository: LumeWeb/pinner-cli

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