inspect: add a per-inspector timeout (default 10m)

Inspectors previously ran under a plain cancel context with no deadline, so a stuck agent could hang the review forever. Each inspector now runs under its own context.WithTimeout (RunConfig.InspectorTimeout, default 10m via defaultInspectorTimeout, overridable with --timeout). On timeout the inspector's process is killed and it is marked failed-by-timeout; sibling inspectors and the judge proceed. A parent cancellation (Ctrl+C) is still classified as cancelled, not timed out.

• RunConfig.InspectorTimeout + inspectorTimeout() default helper.
• Run and RunMulti wrap each Start in a per-agent deadline and detect DeadlineExceeded (vs parent cancel) to set the failed-by-timeout error.
• --timeout duration flag (default 10m) wired through runReview to both the single- and multi-inspector paths.
• Tests: Run times out a hanging inspector; RunMulti times out one inspector while a sibling still succeeds.
• Docs updated (command surface + architecture note).