feat: write output to file

[Ullaakut]

Goal of this PR

Fixes #360

• Adds an option -o or --output-file to specify an output file. Results are written in JSON.
• Updates documentation accordingly

[Copilot]

Pull Request Overview

Adds the ability to export scan results to a JSON file via a new CLI flag and implements the underlying write logic.

• Introduces Scanner.Write to serialize streams to JSON and write to a file
• Adds an -o, --output-file flag in the main command to specify the output path
• Updates README to document the new output-file option

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
summary.go	Added Write method on Scanner for JSON output
cmd/cameradar/cameradar.go	Defined output-file flag handling and call to Write
README.md	Documented the -o, --output-file option

Comments suppressed due to low confidence (2)

README.md:124

• The README entry does not specify a default path or indicate how the absence of this flag is handled. Consider clarifying the default behavior or adding the default filename/path in the description.

* **"-o, --output-file"**: Output scan results as a JSON file. If not specified, results are not written to a file.

summary.go:74

• There are no unit tests for the new Write method. Adding tests for successful JSON output and error paths (e.g., marshal failure or write errors) will improve reliability.

func (s *Scanner) Write(wc io.WriteCloser, streams []Stream) error {