Remove the standalone GET /api/unit/runtimes endpoint in favour of
embedding runtime directly in existing responses:
- GET /api/unit → each item now includes `runtime` field
- GET /api/unit/:id → returns UnitWithRuntime
- GET /api/unit/:id/detail → UnitDetail now includes `runtime`
runtime is null when the engine has not yet initialised the unit.
Frontend loadUnits() reads the embedded runtime field to populate
state.runtimes — one request instead of two.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
caoqianming
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