Add --copy flag to copy response body to clipboard

[ryanfowler]

Add a new --copy flag that copies the raw response body to the system clipboard while still printing output to stdout normally. Supports pbcopy (macOS), clip.exe (Windows), and wl-copy/xclip/xsel (Linux).

Includes config file support (copy = true), streaming response detection (warns and skips for SSE/NDJSON), a 16MB buffer limit, and integration tests.

[Copilot]

Pull request overview

This PR adds a --copy flag that copies HTTP response bodies to the system clipboard while maintaining normal stdout output. The implementation includes configuration file support, platform-specific clipboard command detection, streaming response handling, and buffer size limits.

Changes:

• Adds --copy CLI flag and copy config file option with boolean parsing
• Implements clipboard copying with platform detection (pbcopy/clip.exe/wl-copy/xclip/xsel)
• Adds streaming detection to skip SSE/NDJSON responses with warnings
• Implements 16MB buffer limit for clipboard operations
• Adds integration tests covering stdout preservation, file output compatibility, HEAD requests, and silent mode

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
main.go	Integrates Copy field from config into Request struct
internal/fetch/fetch.go	Adds Copy field to Request and integrates clipboard copier lifecycle
internal/fetch/clipboard.go	Implements clipboard copying logic with platform detection and streaming checks
internal/config/config.go	Adds Copy config field with merge logic and boolean parsing
internal/cli/app.go	Adds --copy CLI flag definition
integration/integration_test.go	Adds integration tests for copy functionality
docs/configuration.md	Documents copy config option
docs/cli-reference.md	Documents --copy CLI flag with platform requirements

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