Support --copy for streaming responses (SSE, NDJSON, gRPC)

[ryanfowler]

Replace the upfront rejection of --copy for streaming content types with a limitedBuffer writer that captures up to 1 MiB as the stream is consumed. If the response exceeds the limit, a warning is printed and the copy is skipped instead of silently truncating data.

[Copilot]

Pull request overview

This PR enables clipboard copying for streaming responses (SSE, NDJSON, gRPC) by replacing the upfront rejection with a buffered capture approach. Previously, --copy would fail immediately for streaming content types; now it captures up to 1 MiB of the response as it streams, warning users only if the limit is exceeded.

Changes:

• Introduced limitedBuffer writer to capture streaming data up to 1 MiB without blocking or truncating
• Removed content-type checks that prevented --copy for streaming responses
• Added comprehensive unit tests for the limitedBuffer behavior
• Updated documentation to reflect support for streaming responses

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/fetch/clipboard.go	Implements limitedBuffer and integrates it into clipboard copying logic to support streaming responses
internal/fetch/clipboard_test.go	Adds unit tests for limitedBuffer covering various overflow and boundary scenarios
integration/integration_test.go	Adds integration tests verifying --copy works with SSE and NDJSON responses
docs/cli-reference.md	Updates documentation to note streaming support and the 1 MiB limit

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