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/vexer/README.md

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+# StellaOps Vexer
+
+Vexer computes deterministic consensus across VEX claims, preserving conflicts and producing attestable evidence for policy suppression.
+
+## Responsibilities
+- Ingest Excititor observations and compute per-product consensus snapshots.
+- Provide APIs for querying canonical VEX positions and conflict sets.
+- Publish exports and DSSE-ready digests for downstream consumption.
+- Keep provenance weights and disagreement metadata.
+
+## Key components
+- Consensus engine and API host in `StellaOps.Vexer.*` (to-be-implemented).
+- Storage schema for consensus graphs.
+- Integration hooks for Policy Engine suppression logic.
+
+## Integrations & dependencies
+- Excititor for raw observations.
+- Policy Engine and UI for suppression stories.
+- CLI for evidence inspection.
+
+## Operational notes
+- Deterministic consensus algorithms (see architecture).
+- Planned telemetry for disagreement counts and freshness.
+- Offline exports aligning with Concelier/Excititor timelines.
+
+## Related resources
+- ./scoring.md
+
+## Backlog references
+- DOCS-VEXER backlog referenced in architecture doc.
+- CLI parity tracked in ../../TASKS.md (CLI-GRAPH/VEX stories).
+
+## Epic alignment
+- **Epic 7 – VEX Consensus Lens:** deliver trust-weighted consensus snapshots, disagreement metadata, and explain APIs.