feat: propagate actions dependencies

[nodeselector]

Propagate the actions dependencies into the actions resolution call.

We technically don't need to recurse in order to resolve all the actions dependencies with a well-formed pinned job and could reduce the round trips for resolution. I will leave this to another PR.

ref https://github.com/github/actions-dispatch/issues/559

[Copilot]

Pull request overview

Adds end-to-end plumbing for workflow-level action dependency pins (“lockfile entries”) so they can be forwarded into the Launch action-resolution request.

Changes:

• Introduce dependencies on AgentJobRequestMessage and surface it via ExecutionContext.Global.
• Extend action-resolution request contracts to include actions_dependencies, and pass dependencies to Launch resolution calls.
• Add L0 tests validating AgentJobRequestMessage deserialization of dependencies.

Show a summary per file

File	Description
src/Runner.Worker/ActionManager.cs	Forwards workflow dependencies into the Launch action resolution request.
src/Runner.Worker/ExecutionContext.cs	Copies workflow dependencies from the job message into GlobalContext.
src/Runner.Worker/GlobalContext.cs	Adds a place to store workflow-level action dependencies for the job.
src/Sdk/DTPipelines/Pipelines/AgentJobRequestMessage.cs	Adds serialized dependencies field with lazy-initialized public accessor.
src/Sdk/DTWebApi/WebApi/ActionReferenceList.cs	Adds Dependencies to the action reference list model.
src/Sdk/WebApi/WebApi/LaunchContracts.cs	Adds actions_dependencies to the Launch request payload contract.
src/Sdk/WebApi/WebApi/LaunchHttpClient.cs	Maps ActionReferenceList.Dependencies into Launch’s actions_dependencies field.
src/Test/L0/Sdk/RSWebApi/AgentJobRequestMessageL0.cs	Adds L0 tests for dependencies deserialization behavior.
src/Test/L0/Worker/ActionManagerL0.cs	Minor test setup adjustment (dictionary initialization).

Copilot's findings

• Files reviewed: 9/9 changed files
• Comments generated: 2