feat(docs): Add comprehensive documentation for Vexer, Vulnerability Explorer, and Zastava modules

- Introduced AGENTS.md, README.md, TASKS.md, and implementation_plan.md for Vexer, detailing mission, responsibilities, key components, and operational notes.
- Established similar documentation structure for Vulnerability Explorer and Zastava modules, including their respective workflows, integrations, and observability notes.
- Created risk scoring profiles documentation outlining the core workflow, factor model, governance, and deliverables.
- Ensured all modules adhere to the Aggregation-Only Contract and maintain determinism and provenance in outputs.

docs/modules/scheduler/README.md

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+# StellaOps Scheduler
+
+Scheduler detects advisory/VEX deltas, computes impact windows, and orchestrates re-evaluations across Scanner and Policy Engine.
+
+## Responsibilities
+- Maintain impact cursors and queues for re-scan/re-evaluate jobs.
+- Expose APIs for policy-triggered rechecks and runtime hooks.
+- Emit DSSE-backed completion events for downstream consumers (UI, Notify).
+- Provide SLA-aware retry logic with deterministic evaluation windows.
+
+## Key components
+- `StellaOps.Scheduler.WebService` control plane.
+- `StellaOps.Scheduler.Worker` job executor.
+- Shared libraries under `StellaOps.Scheduler.*`.
+
+## Integrations & dependencies
+- MongoDB for impact models.
+- Redis/NATS for queueing.
+- Policy Engine, Scanner, Notify.
+
+## Operational notes
+- Monitoring assets in ./operations/worker-grafana-dashboard.json & worker-prometheus-rules.yaml.
+- Operational runbook ./operations/worker.md.
+
+## Related resources
+- ./operations/worker.md
+- ./operations/worker-grafana-dashboard.json
+- ./operations/worker-prometheus-rules.yaml
+
+## Backlog references
+- SCHED-MODELS-20-001 (policy run DTOs) and related tasks in ../../TASKS.md.
+- Scheduler observability follow-ups in src/Scheduler/**/TASKS.md.
+
+## Epic alignment
+- **Epic 2 – Policy Engine & Editor:** orchestrate incremental re-evaluation and simulation runs when raw facts or policies change.
+- **Epic 6 – Vulnerability Explorer:** feed triage workflows with up-to-date job status, explain traces, and ledger hooks.
+- **Epic 9 – Orchestrator Dashboard:** expose job telemetry, throttling, and replay controls through orchestration dashboards.