Add SECAM (method 1) option to launcher GUI. - #347

Checklist

• I have searched the open pull requests to confirm this change has not already been submitted.
• My branch is up to date with the target branch.
• I have tested my changes and all existing tests pass.
• I have updated documentation where necessary.
• My code follows the project's coding standards (see CONTRIBUTING.md).

Description

Adds SECAM to the system dropdown in decode-launcher.

Motivation

#337 added support for decoding VHS SECAM (French recording method, method 1) and re-encoding as studio SECAM in the Y/C-separated TBC outputs. It was added to the CLI and vhs-decode-gui, but not added to decode-launcher.

Testing

• All existing tests pass (pytest --output-on-failure)
• Tested manually with: trying out samples from various systems including SECAM, MESCAM, NTSC, PAL.
• New tests added for:

Screenshots (if applicable)