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/scanner/README.md

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+# StellaOps Scanner
+
+Scanner analyses container images layer-by-layer, producing deterministic SBOM fragments, diffs, and signed reports.
+
+## Responsibilities
+- Expose APIs (WebService) for scan orchestration, diffing, and artifact retrieval.
+- Run Worker analyzers for OS, language, and native ecosystems with restart-only plug-ins.
+- Store SBOM fragments and artifacts in RustFS/object storage.
+- Publish DSSE-ready metadata for Signer/Attestor and downstream policy evaluation.
+
+## Key components
+- `StellaOps.Scanner.WebService` minimal API host.
+- `StellaOps.Scanner.Worker` analyzer executor.
+- Analyzer libraries under `StellaOps.Scanner.Analyzers.*`.
+
+## Integrations & dependencies
+- Scheduler for job intake and retries.
+- Policy Engine for evidence handoff.
+- Export Center / Offline Kit for artifact packaging.
+
+## Operational notes
+- CAS caches, bounded retries, DSSE integration.
+- Monitoring dashboards (see ./operations/analyzers-grafana-dashboard.json).
+- RustFS migration playbook.
+
+## Related resources
+- ./operations/analyzers.md
+- ./operations/analyzers-grafana-dashboard.json
+- ./operations/rustfs-migration.md
+- ./operations/entrypoint.md
+
+## Backlog references
+- DOCS-SCANNER updates tracked in ../../TASKS.md.
+- Analyzer parity work in src/Scanner/**/TASKS.md.
+
+## Epic alignment
+- **Epic 6 – Vulnerability Explorer:** provide policy-aware scan outputs, explain traces, and findings ledger hooks for triage workflows.
+- **Epic 10 – Export Center:** generate export-ready artefacts, manifests, and DSSE metadata for bundles.