feat(agent): log restore controller phase timings

[hutm]

Problem

Restore timing starts inside the executor, leaving controller work such as preflight validation and finalizer updates unaccounted for.

Why

Without controller-stage timing, operators cannot tell whether a slow restore spent time preparing the request or executing CRIU and CUDA restore.

Change

Log one structured timing summary per controller pass with total, preflight, finalizer, and restore durations, plus the stage where the pass returned.

Testing

• Added coverage for the structured timing fields on a preflight failure.
• Ran the complete agent test suite.

Fixes #350

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