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/operations/rustfs-migration.md

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+# Scanner Artifact Store Migration (MinIO → RustFS)
+
+## Overview
+
+Sprint 11 introduces **RustFS** as the default artifact store for the Scanner plane. Existing
+deployments running MinIO (or any S3-compatible backend) must migrate stored SBOM artefacts to RustFS
+before switching the Scanner hosts to `scanner.artifactStore.driver = "rustfs"`.
+
+This runbook covers the recommended migration workflow and validation steps.
+
+## Prerequisites
+
+- RustFS service deployed and reachable from the Scanner control plane (`http(s)://rustfs:8080`).
+- Existing MinIO/S3 credentials with read access to the current bucket.
+- CLI environment with the StellaOps source tree (for the migration tool) and `dotnet 10` SDK.
+- Maintenance window sized to copy all artefacts (migration is read-only on the source bucket).
+
+## 1. Snapshot source bucket (optional but recommended)
+
+If the MinIO deployment offers versioning or snapshots, take one before migrating. For non-versioned
+deployments, capture an external backup (e.g., `mc mirror` to offline storage).
+
+## 2. Dry-run the migrator
+
+```
+dotnet run --project src/Tools/RustFsMigrator -- \
+  --s3-bucket scanner-artifacts \
+  --s3-endpoint http://stellaops-minio:9000 \
+  --s3-access-key stellaops \
+  --s3-secret-key dev-minio-secret \
+  --rustfs-endpoint http://stellaops-rustfs:8080 \
+  --rustfs-bucket scanner-artifacts \
+  --prefix scanner/ \
+  --dry-run
+```
+
+The dry-run enumerates keys and reports the object count without writing to RustFS. Use this to
+estimate migration time.
+
+## 3. Execute migration
+
+Remove the `--dry-run` flag to copy data. Optional flags:
+
+- `--immutable` – mark all migrated objects as immutable (`X-RustFS-Immutable`).
+- `--retain-days 365` – request retention (in days) via `X-RustFS-Retain-Seconds`.
+- `--rustfs-api-key-header` / `--rustfs-api-key` – provide auth headers when RustFS is protected.
+
+The tool streams each object from S3 and performs an idempotent `PUT` to RustFS preserving the key
+structure (e.g., `scanner/layers/<sha256>/sbom.cdx.json.zst`).
+
+## 4. Verify sample objects
+
+Pick a handful of SBOM digests and confirm:
+
+1. `GET /api/v1/buckets/<bucket>/objects/<key>` returns the expected payload (size + SHA-256).
+2. Scanner WebService configured with `scanner.artifactStore.driver = "rustfs"` can fetch the same
+   artefacts (Smoke test: `GET /api/v1/scanner/sboms/<digest>?format=cdx-json`).
+
+## 5. Switch Scanner hosts
+
+Update configuration (Helm/Compose/environment) to set:
+
+```
+scanner:
+  artifactStore:
+    driver: rustfs
+    endpoint: http://stellaops-rustfs:8080
+    bucket: scanner-artifacts
+    timeoutSeconds: 30
+```
+
+Redeploy Scanner WebService and Worker. Monitor logs for `RustFS` upload/download messages and
+Prometheus scrape (`rustfs_requests_total`).
+
+## 6. Cleanup legacy MinIO (optional)
+
+After a complete migration and validation period, decommission the MinIO bucket or repurpose it for
+other components (Concelier still supports S3). Ensure backups reference RustFS snapshots going
+forward.
+
+## Troubleshooting
+
+- **Uploads fail (HTTP 4xx/5xx):** Check RustFS logs and confirm API key headers. Re-run the migrator
+  for the affected keys.
+- **Missing objects post-cutover:** Re-run the migrator with the specific `--prefix`. The tool is
+  idempotent and safely overwrites existing objects.
+- **Performance tuning:** Run multiple instances of the migrator with disjoint prefixes if needed; the
+  RustFS API is stateless and supports parallel PUTs.