test: add cloud-specific pipeline unit tests for missing-model pipeline with isCloud mocking strategy

[coderabbitai]

Follow-up from PR #11751

Context:
PR #11751 (#11751) added src/platform/missingModel/missingModelPipeline.ts and its test file src/platform/missingModel/missingModelPipeline.test.ts. Cloud-specific pipeline unit tests were deferred because they require a separate isCloud mocking strategy.

Task:
Design and implement a suitable isCloud mocking strategy for unit tests, then add cloud-specific unit test coverage for the missing-model pipeline (e.g., cloud asset verification flow, abort-guarded behavior in cloud mode, surfacing after cloud verification).

Relevant files:

• src/platform/missingModel/missingModelPipeline.ts
• src/platform/missingModel/missingModelPipeline.test.ts

Requested by: @jaeone94 in #11751

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