test(queue): add job metadata and queue message serialization tests

[jdfalk]

Motivation

• Increase Go test coverage by adding focused unit tests for queue job implementations in pkg/queue while avoiding the previously-tested types.go file.
• Picked pkg/queue/jobs.go (randomized selection) because it contains job metadata, message serialization, and execution paths that exercise multiple components.

Description

• Added pkg/queue/jobs_test.go with unit tests covering SingleFileJob and BatchFilesJob metadata, QueueMessage payload serialization, and Description()/ID()/Type() behaviors.
• Added tests that verify QueueMessage payloads are marshalled to jobpb.TranslationJob via anypb.UnmarshalTo using proto.UnmarshalOptions.
• Added tests asserting Execute returns path validation errors for relative (invalid) paths to exercise integration with security.ValidateAndSanitizePath without changing production code.
• No production files were modified; this PR only adds tests.

Testing

• Ran go test ./pkg/queue which completed successfully.
• The new test file is pkg/queue/jobs_test.go and it passed locally under the repository test run.

Files that may be involved or touched by other contributors to avoid conflicts: pkg/queue/jobs.go, pkg/queue/queue.go, pkg/queue/message.go (protobuf wrappers), pkg/subtitles/translatefile.go, pkg/translator/translator.go, pkg/security/security.go, and the generated proto types under pkg/jobpb.

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Codex Task

[jdfalk]

@copilot rebase and force push this and fix the merge conflicts from the rebase.

[Copilot]

@jdfalk I've opened a new pull request, #2054, to work on those changes. Once the pull request is ready, I'll request review from you.