feat(FN-3391): persist evaluator evidence with score categories

- Add eval score category types and exports in core with store support and coverage
- Implement engine evaluator evidence extraction and persistence with dedicated tests
- Update evaluator flow and cron wiring to record evidence alongside eval runs
- Refresh architecture, storage, and eval docs for evidence and categorization behavior

Fusion-Task-Id: FN-3391

packages/engine/src/index.ts

@@ -12,6 +12,7 @@ export {
 export { AgentSemaphore, PRIORITY_MERGE, PRIORITY_EXECUTE, PRIORITY_SPECIFY } from "./concurrency.js";
 export { TriageProcessor, type TriageProcessorOptions } from "./triage.js";
 export { TaskExecutor, type TaskExecutorOptions } from "./executor.js";
+export { collectTaskEvaluationEvidence } from "./evaluator-evidence.js";
 export { Scheduler, type SchedulerOptions } from "./scheduler.js";
 export { MissionAutopilot, type MissionAutopilotOptions } from "./mission-autopilot.js";
 export { MissionExecutionLoop, type MissionExecutionLoopOptions, type ValidationResult, loopLog } from "./mission-execution-loop.js";