Extract the engine wiring (YouTube source, AI-router summarizer, store sink)
into buildProcessor, shared by cmdRun and cmdServe. It returns (nil, nil) — not
an error — on incomplete config, which is the queue-only fallback for serve.
engineProcessor adapts the engine to web.Processor: load the video row, run the
engine, clear the manual queue flag on a produced summary (mirrors the runner).
cmdServe wires it onto web.App.Processor; cmdRun reuses buildProcessor so the
wiring is no longer duplicated.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
