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/vex-lens/README.md

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+# StellaOps VEX Consensus Lens
+
+VEX Lens computes deterministic consensus across conflicting VEX statements while preserving raw provenance.
+
+## Responsibilities
+- Ingest VEX evidence from Excititor and align it to SBOM inventory.
+- Apply issuer trust weights, freshness rules, and policy-defined tie breakers.
+- Publish consensus snapshots and disagreement metadata for Policy Engine and Explorer surfaces.
+- Expose APIs for explainability and offline bundle exports.
+
+## Key components
+- Consensus computation service and job pipeline.
+- Consensus store with versioned snapshots.
+- Explain trace generator for disagreements.
+
+## Integrations & dependencies
+- Excititor for raw VEX ingestion.
+- Policy Engine for applying consensus in suppression flows.
+- Vulnerability Explorer and Advisory AI for evidence overlays.
+
+## Operational notes
+- Trust model configuration and issuer scoring dashboards.
+- Offline kit packaging of consensus snapshots.
+- Telemetry on issuer coverage and disagreement counts.
+
+## Epic alignment
+- Epic 7: VEX Consensus Lens.
+- Lens implementation stories tracked in ../../TASKS.md.