Add `--output` / `-o` flag to save response body to file

[kavix]

Description

Users currently pipe output to files, but this captures formatted/colored output rather than raw response. A dedicated flag should save the raw body.

Proposed Implementation

kurl https://api.example.com/image.png -o image.png

kurl https://api.example.com/data.json -o ./data.json --no-color

Why this matters

Piping formatted JSON with color codes to a file corrupts the data. A dedicated flag ensures raw binary/text output.

Acceptance Criteria

• Add -o / --output flag
• Save raw response body (not formatted/colored)
• Create parent directories if they don't exist
• Show download progress for large files (optional)
• Add test coverage

Getting Started

Intercept the response body before formatting. Write to io.Writer that either goes to stdout or the file based on flag.

---